I feel like I know the answer already, but I’d like unbiased answers, so why not here?

For some background context: My daughter’s father, and his family, are not around. We have made an extremely close bond with another family and they have been involved in her life since she was an infant. They are who we consider her grandparents and aunt.

I, (late 30’s F) have a daughter (8F), S, who is very close with her aunt (late 20’s F), B. While we’re not blood related, we call each other “sisters”. Throughout my daughter’s life, B has been very concerned with her many relationships and trying to hold on to men that have been verbally, emotionally, and even physically abusive. She will say that S comes first no matter what, then not speak to, or see, S for weeks at a time. When the relationships end, S is right back to being her #1 priority and she wants to see S, pick S up to go do fun things and have her spend the night.

Recently, B decided to end her most recent relationship with her partner, C. Their relationship was tumultuous, he did not treat B well and also did not treat my daughter well. Once I found out how S was being treated, I went into “mama bear” mode and shut it down. B & C’s relationship continued, my daughter was treated better, but B was still being abused. B was using S almost as a human shield, and wanted S around so C wouldn’t be abusive. She promised S they’d do all kinds of things once C was gone and really got my daughter’s hopes up.

Finally, B decided to end things with C, but it was all in an effort to immediately re-start a relationship with an ex-boyfriend of hers. This former ex has a small child and B has immediately started acting like this child’s mother. She no longer spends time with S unless myself, and B’s mom, harass her about it. She would rather spend time with the new boyfriend’s child. When S calls B, she won’t answer the phone and recently told S that she can’t “come first any more” because of the new child in B’s life. When B was confronted about saying this, she started crying and said she “didn’t mean it like that”, but didn’t clarify how it was actually meant.

B is extremely sensitive, and is very quick to go to her parents when she feels disrespected, has her feelings hurt, or even FEELS as if these things have happened. Her parents are very protective of her (as any parent should be) but I feel I’m walking a thin line here. Anything I say could/will be relayed back to her parents and I don’t want to cause a rift between all of us, but I also can’t stand seeing S upset and disappointed. I’ve talked to B’s mother about this, and while she is unhappy with B’s behavior, B doesn’t seem to get it, or just doesn’t care.

So, AITA here? I’m admittedly a people pleaser, and I’m trying hard to work through that. It’s just after so many years of being this way, I almost don’t know when I’m in the right, or even the wrong.