aw man econdiva, that's a lot
let me begin with I'm glad you took the time in portugal, and i'm sorry about your mom's strokes or whatever the whole story is
I think the hospital stay will lead you to resources, like the doctors and social workers, who will know where your mom should stay next. it won't be somebody's house. it wil lbe like a nursing home for people who need assistance with their daily living and physical therapy for whatever damage the stroke did to balance, walking, dressing, eating... there is a huge range and i'm sure it's too soon to know your mom's new capabilities and what level of support she needs and for how long. I just want to be loud and clear that there are professionals who provide this expert, safe, care, in specific locations that would be covered by her insurance or medicaid/medicare, and that this hospital stay needs to end with your mom in the appropriate setting, NOT her sister's place where this happened and NOT your place where it's a huge burden on you and besides, you're not a nurse or physical therapist. IMO your role to help support her is by advocating at the hospital and communciating to the social workers about where to go next.
the tax thing... does this mean your mom did not file her own return? does she have enough income that she should have? if you were getting involved in her finances at all, I think what i suggest is file/refile her return, as a non-dependent if that is the truth. the IRS is more than capable of noticing and investigating. there is no need to talk about this in person.
i agree the real takeaway about the tax issue is now you know the aunt will use your mom for money. perhaps she's filed for other social programs on her behalf, like food stamps? who knows. or opened credit cards now that she has her social plus address? That crap won't stop just bc your mom moves out. I don't mean to slander your aunt. maybe the tax thing was simply ignorance of the rules. i'm just saying if you want an actionable thing here, it isn't confronting the aunt and it's not moving your mom out. it's filing her taxes correctly and freezing her credit. and yes *be careful* not to get legally entangled. don't put your name on any of her accounts thinking that will help. don't sign anything at the hospital about being liable for her care. you're the family contact for medical decisions not billing ones.
damn, and good luck!