Hey Jerred,
Tell her when you feel comfortable. No one here can can say you should do it now or later. This is a decision that only you can make.
However, I can totally relate with where you are coming from. I live with my mom as well and feel the need to come out because otherwise I can't move forward. Yet, I am terrified to do so because I am somewhat dependent on her and would have no where else to go. Nonetheless, I know what has to be done and have been working on becoming courageous and plan on saying something soon. Personally, I have decided to let mothers day pass before I consider coming out. I love my mom and want her to have a great day. Coming out beforehand will make some difficulties and I don't want to spoil her special day. My mom always looks forward to this day, and I want her to fully enjoy it. You situation may be very different, but this is something that only you can decide. If you could wait though, I think that might be easier for her.