I have been feeling really let down lately by my sister.
I'm always there for her when she needs a babysitter or wants company, I always pick up the phone when she calls and reply to her texts.
But when it comes to me, it's like I'm invisible, until she needs me. She never answers my calls, or returns them, she doesn't text me back, and she uses my love of my nephews to manipulate me into doing what she wants.

I've spoken to my T about it because my biggest problem is saying no. When I was 15 I ran away from my mother's house due to my stepdad, I moved into my dad's house where my sister lived. We've always been close, more so after my first nephew was born. 8.5 years into the future to this day, I feel a building sense of resentment towards her. I babysit at least 5 times a week, and even if I've had an awful session in therapy, it doesn't matter if she needs a babysitter. She'll beg me to pick the children up from school because she's busy and there's NO ONE else to pick them up, says she'll be an hour and doesn't show up for 6 hours. She guilt trips me and manipulates me because she knows I'd never see those boys upset or neglected in any way shape or form.

Trying to explain I've had a bad session, or no sleep or a flashback means very little to her but when it comes to her emotional wellbeing it's a matter of family knowledge. It's my sisters show and I'm just a part of it. I was diagnosed with PTSD, BDD, anorexia, depression, and blackout disassociation. When I have a bad session it usually means I've been unconscious due to a form of disassociation, or like anyone else, it was a particularly hard topic or day. I've tried talking to my sister, at this point I don't even want her support, I'd just like some recognition that I am in fact her sister and not an unpaid, overused babysitter.

How do I say no to my sister when she doesn't listen or seem to care about what's going on in my life?

* I have tried to say no on one occasion and I failed miserably. I would've been responsible for the children not going on vacation so I caved.