Sister claims she has POA but she won't show it to me. What should I do?

First and foremost, if your sister has POA, she is under no legal obligation to prove it to you, though morally and ethically, it would be the right thing to do. The only way to force that issue would be to retain the services of an attorney and try to force her to show it to you. I don't know how successful you would be with that, but an attorney specializing in elder law would be able to discuss that with you.

Secondly, if Mom is on Medicaid now (not Medicare - MedicAID), or will be in the near future, using Mom's money to remodel the home so it can be rented out (thus, causing income) could be a problem. Medicaid does a 5-year lookback, and if Mom has divested (sold/given away) any assets or has income in excess of what Medicaid allows, there is going to be either a penalty period or a spend-down required before she will be qualified for Medicaid.

If Mom is saying she didn't sign a POA, that may be true - or she may not remember, since you say she has dementia. She may have signed in a lucid moment and then forgotten she did it.

I can't imagine why Sister won't show it to you. Susan is right -- she doesn't have to -- but if she has such a document, showing it would make sense.

If your mother is still lucid enough to understand the concept of POA and if she does not want to have Sister hold that authority, she can simply revoke the so-called POA and assign it to someone else, or to nobody.

Is Medicaid in the picture, now or in the future?

I would think these documents would be needed to move in..When my mother moved in AL we had to bring POA document and Advanced Health Directive...