Can you not just cut to the chase and mention it to her? I mean, rather than beat about the bush and hope she will tell you (which I don't think she will given what you mentioned yesterday), why not just ask her point blank.
I'm so sorry that you are going through this, it's such a shitty situation. And I think a support group is a great idea. Having other people to lean on who completely know what you are going through is huge.
Good point. It honestly sounds like she needs someone there with her, and not your dad since he sounds like he is a softy when it comes to her (which is understandable) to really listen and mention things she leaves out. Hell, i could use this sometimes too.
I'm sending you a big hug and I hope I am not coming off as a bossy pants. You seem like a really good daughter to your parents.