In law rant!!!!

This is going to be a long post. So I apologize......... So my sister in law is... Well was my best friend. We met a few years ago like okay maybe 8 years ago. We became really good friends before me and her brother got married. I felt like she was a real sister to me. And I treat her daughter and son like my own blood. Me and my husband have recently moved to Pennsylvania to be closer to his family in New Jersey. My sister in law is in a long term relationship with a man. I don't judge people for what they do and who they choose to be with. My sister in law & her boy each have kids from other Relationships. My sister in laws daughter... Well shall say my niece Is always being picked on by her step dads kids. You know typical step sibiling behavior. My poor niece is always getting the shitty end of everything. It's seems like she gets last of what's left her. Her mother my sister in law gets child support. But none of that money gets used for her instead it gets used towards the other kids.  Her mother and step father don't make it any easier. Bc them 2 are always fighting. And it's not just little fights no I'm talking extreme fights to the point where my sister in law leaves and takes my niece with her and has her roaming jersey streets. Just recently my niece has been making comments that she wants to live with her dad back in Texas Bc she's not happy here. Keep in mind she's only 9 years old. My sister in law is thinking about letting it happen Bc she doesn't want to leave her boyfriend of 4 years. She'd rather lose her daughter then making an effort or change to keep her and make her happy.