Am I wrong?

I have a 6 year old step child that love like my own but I can't see her neither can her father because her mother is into a lot of drama... And she mad that I had my son after I had him he has seizures (he is now 1 he has therapies to help him develop he does have developmental delays) and she would said "she hope he die" or while I was pregnant would she would say "I hope he dies in your womb". Just mean and hurtful things... I love my step child but I want a daugther that I can call my own and be around all the time with out the drama of someone calling me out my name or if my step daugther calls my step mommy or even mommy she get popped or slapped... It's a very sad situation but i feel like I'm wrong for wanting my own daugther...