Where do I start looking for care?

There may be an APS (Adult Protective Services) or similar authority in your town, you may need to contact them to initiate a complaint and then they will check the situation out.

Have you witnessed the horrible care, or are you being told about it? I'm sure if you met my MIL she would tell you that she is being treated horribly by her family - not letting her have her meds, no food in her house and unable to get to town, etc. But the truth would be that her medication is brought on a daily basis - one day's supply only (so she can't mess it up too badly, but yes, we are not letting her have all the medications/bottles in her home anymore - she has made too many mixups with them.) She gets taken to town once a week for groceries (but doesn't always like what in in her cabinets by the end of the week - we all have days like that, when nothing 'sounds good for dinner')

I have more examples like this, but the point is, what the elder person says is not always the most accurate reflection of what is going on. So do talk with the daughter and see what she has to say before you proceed too far.

If you see horrible care, encourage the patient or POA to file a complaint.

As an outsider who has neither financial or medical POA you really don't have a lot of leverage to make any changes. If you feel she is vulnerable you can make a report to her local Agency on Aging and ask that her care is reviewed.