The older sister has POA for her mother in assisted living, how do we know what that POA says?

A POA is only a public record if it was recorded, which would be a requirement if the attorney-in-fact/agent conducted a real estate transaction on the mother's behalf (as to the financial POA). As to a healthcare POA, it need only be shared with those who request it in their capacity as a healthcare provider or the holder of the healthcare records. I've never seen a healthcare POA on public record.

I think I'm a little confused - who holds what POA? Does your wife hold the healthcare POA or the financial POA? Or does the hostile older sister hold both POAs? I'm responding in the thought that sister in charge has the POAs.

As to the facility denying access to records - no one would release healthcare information unless they had the required authority. And even if one held a healthcare POA, they may not necessarily release information to the POA agent if the principal is capable of handling her own health care at that particular point in time. It depends on how the healthcare POA was written. If your wife isn't the healthcare POA or her mother hasn't specifically authorized the release of medical information to your wife, the facility is correct that they cannot release information to her.

As to who can attend medical visits - doesn't that right reside with the mother? If the mother wants someone to go with her and is competent to make that decision, she certainly has the right have whomever she'd like with her.

The older sister has power of attorney, unspecified, and a background in law.
The younger sister, who is the OP's wife, does not have power of attorney and is not the mother's health care proxy and yet has a background in healthcare.

Which leads me to wonder whether the mother was (correctly) advised by her older daughter to draw up POA documentation in good time, but sadly not assisted to think the issues through in the round.

Without power of attorney or the mother's own authorisation (if the mother still has the mental capacity to give it) then the OP's wife cannot be provided with confidential information about her mother and does not have any right to insist on accompanying her to healthcare appointments; nor would she have any right to see the POA documentation, although the ALF must have done at some point... there must be a way of requesting that its validity be checked, though I don't know what that would be. And it could be argued that it is very much in the mother's best interests to be accompanied by a daughter with demonstrable expertise in healthcare.

It is a pity that there is not better communication between the sisters. But in the absence of that, you had better take legal advice on, perhaps, for example, challenging the validity of the older sister's POA if you have grounds to believe that the older sister exercised undue influence during its creation; or on an application for guardianship if you genuinely believe and can demonstrate that this would be in the mother's best interest. But tussles like this are expensive and destructive - also lucrative for lawyers, so choose your legal adviser with great care.

What does your wife want to do? Is she still able to visit her mother? Does she have real concerns about her mother's welfare? Is there any possibility of a rapprochement, even if only to the extent of being civil, with her sister?

This kind of conflict is extremely painful, frustrating, stressful and counterproductive and I'm sorry you're having to deal with it. I hope you're able to find a way forward.

Is it that you want to see the Medical POA or that your wife wants access to medical records, or both? Is there a particular reason why she wants to see the medical records?

Does your wife suspect some malfeasance or irregularity in the treatment of her mother and wants to verify the records for that reason? If she does and she believes there's a serious issue, she could retain a medmal attorney solely for the purpose of getting the records, through a subpoena.

I'm beginning to wonder if there's something else going on between the sisters. Are they both close to the AL facility where their mother is residing? Do both of them visit?

I assume you're aware that there wouldn't be the type of detailed medical records available as there would be if their mother were in rehab or a skilled nursing facility. Sounds like something else is going on.

Thank you for the thoughtful answers. New to this site, I think my previous answer did not get posted. Yes, both sisters are close, although we live farther away. No wealth at all is involved. And the 91-year old mother is getting good care. We only wanted to know if there was a legal basis for lack of communication (HIPA?) but don't consider any legal action. Much to think about, and I learned some from your posts.