She's a cold hearted bitch ! *sister rant*

I have a sister who has 2 children, A 5 year old girl and a 3 year old boy. They both have different fathers she separated with her first partner when my niece was only 2 years old and she separated with her second partner when my nephew wasn't even 1 year old. The reason he separated with her first partner was because he would always rather spent time with his friends than with my niece and sister, they were like that for a while until my sister had enough. Now with her second partner she separated from him because SHE was partying too much. Literally like 3 months after having my nephew she began going out every other weekend with her friends to eat dinner and have some drinks and she would leave BOTH kids with my nephews dad (her second partner). She began doing it more frequently where she began going to clubs and not even coming home to sleep. He had enough and left her and took their son ( my nephew wasn't even 1 year old) and she did NOTHING to stop him. So at this point she was single and only had my little niece with her, she didn't change she kept doing her thing and going out even more. She would leave her daughter with anybody just to go get stupid wasted. My nieces dad ended up taking my niece away from my sister too and once again my sister did NOTHING to stop him. She ended up alone no kids no partner because of her stupid decisions. Fast forward to today me and her stopped talking we had a big fight a few weeks ago. It's been 2 years since she lost her kids and she still does nothing to get them back. She has yet another partner which she lives with, she doesn't work, doesn't go to school does absolutely nothing but party. This is the reason why we fought because her lifestyle disgusts me and I'm so disappointed in her. Out of her two kids her daughter lives 1 hour away from her and her son lives 10 minutes away from her. She always posts pictures of her daughter on Facebook, she has her daughter's picture as her screensaver JUST HER DAUGHTER not both her kids. She drives 1 hour away whenever she's bored of partying so much to pick up her daughter and she doesn't even acknowledge or tries to spend time with her son that lives 10 minutes away from her. My nephew's father works 12 hours a day so the one who takes care of my nephew is his grandma, she's a very sick lady always is up and down to her appointments with my nephew and my sister is very well aware of this and does shit about it. She doesn't care she sleeps all day and parties all night !!!! That's her freaking child for Gods sake !!!!! She always shows favoritism towards her first child (my niece) and shows NO emotions or care towards my little nephew !! I'm sick of her shit and I've tried countless of times to talk to her about it but she gets mad and stops talking to me. This time I stopped talking to her ! She stresses me the fuck out . She's a heartless woman, she doesn't deserve to be a mom. In this past year she had some pregnancy scares and all she says "I better not get fucking pregnant because I cant deal with another child". Deal with another child ? You don't even have custody of your first 2 !! Are you retarded ? 😡 and here i am struggling to conceive for the past 3 years. I swear I hate her.