practice the conversation?
there is no practice that can ever prepare me for a conversation with my mother. she nearly always manages to exceed my worst expectations. if the talk is needed, it is better to just do it, without expecting anything, but being prepared for anything. you might meet straight out rejection, maybe not intentional from her side, but a rejection is a rejection whether it originates from hate, stupidity, or ignorance. and that will hurt if it happens.
of course, there is also a chance that your mom is slightly more reflected than my own, and a little more open minded as well. if that's the case, it might actually go well. just don't expect it. people betray your expectations so easily, and that hurts more than if you never expected anything to begin with.
if you love your mother, it will be necessary to sort out this problem, it's the only way you can have an honest and sincere relationship with her. she is unable or unwilling to see or relate to you right now. if that goes on too long, the invisibility will have a negative effect on you, and she will also be unable to see you as you are, and how much you love her.
i hope your situation will be resolved in a good way. not being able to have a sensible conversation with your mom about anything that matters, kind of hurts. a lot. i don't want it to get that bad for you.