Sorry if this is in the wrong group, i didn't know where to post.

I'm so pissed off! Me and my mom took in a family member at birth because neither parent wanted her, they'd rather go to parties, get drunk/high and sleep with strangers. We raised her for 15 years then come home one day and she says she's leaving with someone that isn't biologically related to her (he is unfortunately closely related to me) because his mom is dying and barley has a few years left and if she stays with us she won't get any inheritance! She walked out and my moms seen her 7 times in 10 months, this is a girl that has spent everyday with us for 15 years and she turns her back for money she may or may not inherit in God knows how many years! We find out that the person she is living with is having surgery this week and instead of staying with us for 4 nights she's going to either stay with her father who didn't want her or the old bitch of a woman who is dying and will have to spend 5 hours a day on buses and trains to get to and from school very early morning and late at night while it's dark and me and my mom have no say in it! This is just a very small part of what she's done to us, she's started lying, stealing, and sleeping around in parks since she left us, we don't know who she is anymore, my moms so upset with what she's done but she still loves her, I hate her for what she's done and is still doing to my mom, but there is no getting through to her anymore so I'm ready to wash my hands of her and let her screw up her life as much as she wants to, I won't be here when she needs help though.

Thank you for reading my long rant.

Am I being too harsh or should I just let her get on with it? And what can I do for my mom?