I feel bad for feeling the way I do

Yesterday, my sister called me and told me she was pregnant. She's 26 and already has two children that she can't afford. This will be her 5th pregnancy. She kept two, gave one up for adoption and the 4th ended in miscarriage. She was actively trying and this baby was no accident. She does drugs (smokes weed every single day) and drinks all the time with her children around. She's stressed all the time and can't stand her children. She threatens to send them away. She lives in a two bedroom house and doesn't have room for another baby. She is in a toxic relationship, her and her boyfriend fight constantly about everything. 

I can't help but to feel anger towards her. None of my family is going to be happy about her being pregnant again. But everyone will be over joyed when I share my news. They've been waiting for me to get pregnant.  And I feel like her being pregnant is going to take away some of the excitement about me becoming a mother. I just don't get why she even wants another child. I know I can't stop her from doing what she wants but it still pisses me off. I feel bad for her unborn child because she's not stable enough to take care of her kids. Am I overreacting? I know this sounds really selfish and I feel bad but I can't help how I feel.