So for the last 11 months my girlfriend's daughter (now 3) has been calling her 'mommy', but before that she called her 'dada'.  It was a nice stressfree gradual switch until the little girl's other mother found out and told her that she MUST call her mommy and my girlfriend daddy! 

So since then there were 4 or 5 days that the little one has woken up in the morning and went through the whole morning saying mommy to my girlfriend and then around 1-3 in the afternoon (around nap time) when she gets tired but trys to force herself not to have a nap she starts up with the daddy again.

A few days ago when we were in the car the little one had a tantrum and she wanted a drink.  I handed her the drink but she wouldn't take it she wanted her mommy to hand it to her so she just started shouting daddy.  Everytime I said her name, asked her a question, told her hear is your water she just yelled daddy louder and louder.  I tried to explain to her that her mommy was driving and couldn't give her the water but she just started saying it over and over daddy daddy daddy!  She said daddy about 75 times in 10 minutes.  So we turned the music up and ignored her.  I felt bad but after that it was no longer about the wrong name but just the rude behaviour I mean even if she called mommy 50 times in 10 minutes that is still rude especially the tone of voice she was using. 

So I noticed now that when she wants to co-operate she says mommy.  Like when she wants ice cream she will go over and say 'mommy may I have icecream'?  However when she is mad at me or my girlfriend or just over tired she says daddy just to bug us.  Like 'Mommy may I have ice cream?'  "No you haven't finished you dinner yet".  'Daddy I want ice cream daddy give me ice cream.'  I think this is rude behaviour and I don't know how to get it to stop.  If she said daddy by accident,  'daddy may I have a drink mommy?' or 'da...mo...mommy? may I have a drink'  -then I wouldn't say anything but I think screaming daddy when she doesn't get things HER way is a big no no.

Any tips?  I really don't want to be the evil step-mom but I do want to see her respect her mother/my partner.

How does your partner react to all of this and how do they want to discipline their child? I would think that would be the best yardstick. Do what they do, as long as they are ok with it. Your partner won't have any respect if you do all the disciplining. Instead they will be an angel to be walked over and you a demon to the child. Consistency is totally important, setting boundaries that are enforced equally well by both of you is your best bet. 

If it were my kid I would put her to her room and shut the door (she is 2), for 2 minutes and then ask for an apology. If no, then back to the room etc.. Works a charm (unless she is totally out of it tired, in which case nothing works except gentleness and patience to calm her down). You can't hurt them doing this. We do a three step kind of thing - we ask politely if she would like to do it, then we tell her to do it, then we say do it or she is going to her room, finaly room it is. Unless it is an established rule like hitting in which case it is straight to the room, or we give one warning. If it is in the car or when we are out then it is "once we get home you will go to your room" (they don't forget but won't remind you). As long as you always follow through then it has weight. As soon as you start slipping they are all over it and it stops working. You need to get tough where it matters but fair. The start is tough but it gets easier. You could also use sitting alone in the car as a substitute. Otherwise ignore the bad behaviour like you did, or you could stop the car, hop out and leave them in there for a bit. Just make sure you tell them why you are doing it and what it is they are doing that is unacceptable. Once their time is up that is the end of it, they did their time, they apologised, and things can carry on.

Statements like "in our family we don't hit" are powerful messages. 

I think the name is a secondary issue here. She is probably copying her other mums distaste for her ex when she uses the word daddy i.e. when mum uses it she is angry so I'll use it when I am angry with them. I think your partner and your ex need to come to some agreement or you will always have this problem.

She's three years old and she's had her view of things upset by her other mother's behaviour. If she is displaying what you regard to be rude behaviour it could be a combination of her growing-up and becoming independent plus the confusing situation she now finds herself in.

Maybe she is trying to do the right thing by her other mother by saying daddy but finds that it doesn't elicit the response she expects from your partner and you; she is trying to be good and it's not working. Whatever it is, she is confused and unsettled by the sounds of it. It's not her fault.

If her other mother has the best interests of her daughter at heart then she will not subject her to this sort of stuff. The mother is the only one who can fix this situation, in my opinion. The daughter is just the innocent pawn in all of this. Can you and/or your girlfriend talk to her or get someone else to talk to her? She needs to understand that she is stressing her child by asking for something which is really for her own (the mother's) needs. In time, her daughter will be able to reason and will be wondering why her daddy is a woman while everyone else's daddies are men. Easier to have two (three?) mothers, I think.

Kids are smart but this little one is being asked to carry too much of a burden when  it is the adults who should be shouldering the weight. Good luck.

Yeah.. she sounds like she could be really confused.  She's only three, and at this point between her bio-mom and her bio-dad [your girlfriend] she might not even understand the difference between the word 'mommy' and the word 'daddy,' in terms of gender.  In her eyes, your girlfriend is still the same person and there just happens to be two different words to call her.  It's very confusing when she has to call her daddy around one group of people and mommy around another group- how is she supposed to keep track?  She's only three.

Now, with the later example of her only saying daddy to bug you, that's probably all it is.  To bug you.  Not to disrespect your girlfriend's gender, because she probably has no real idea of that yet, as I said.  Toddlers do lots of things just to bug other people.  That doesn't make it okay, but I also wouldn't overreact, either.  I think the main problem here is that she thinks asking over and over will get her what she wants- I personally would focus on that, not the name thing.  Like "You asked once and I said no.  Asking again will not make me say yes, it will make me sit you in the corner for five minutes."

[This comes from my own experience as the eldest out of countless cousins, lol.  I've seen a lot.]

Hypatia's grandson just turned four, and he's been having to switch back and forth with names all along. He knows Hypatia is his grandmother, and he calls her that. When the rest of the family hears him, they "correct" him and refer to her with the wrong pronoun. He actually does quite well at juggling, considering his age. (He's a very smart kid--takes after his grandmother. )

Once when I saw him, Hypatia told him to tell me who she was. I could tell he wasn't sure which answer he was allowed to give. Eventually he said she was his grandmother. He can see with his own eyes that she's a woman.

As your partner's daughter continues to see her as a woman, she'll probably start wondering why her other mother is using the term "daddy." It's definitely something both parents need to work out though--for their daughter's sake. Screaming children are not my thing though, so I won't venture into that area. 

Thank you, all of this is helpful.

My partner doesn't want to punish her for using the wrong names because she knows that is what her ex is doing and that is what is stressing the child out.  However we are encouraging the mommy word and have told others of the situation.

Apologizing is one of the other big issues we are working on.  The other day the little one ran over my foot with the tricycle and it took her 45 minutes and 3 people to convince her to apologize.  For the past year we have been working hard on getting her to say sorry and be responsible for what her body has done example stepping on someone's fingers by accident.  She has NEVER apologized for words that she has said.

She is just starting to realize that there are men and women, girls and boys.  She honestly thinks my girlfriend is a woman and doesn't know that daddy is a name for a man.  She has said to me before "I have two mommies, one named big mama and one named daddy."  Her bio mom also tells her to call my girlfriend he and him but I have never heard her do this.  so if she is smart enough to know I call my mommy him when I am at my mama's house but I call her her and she at my mommy's house, then eventually she will pick up the mommy daddy thing and maybe one day she will tell her other mom to stop calling her mommy daddy

As for working it out every bit of information between them goes through lawyers so this situation is going to cost a lot of money to solve.