Re: sister's avarice, what are my options?

Did Mom have a will? If so, was sister named Executor?

If no Will then she would have to go to Probate and be assigned Administrator. She can't assume Executorship. As Adminstrator she has to take on similar responsibilities of an Executor. She has to make sure debts are paid. The difference is as Executor the estate is distributed how the person who passed wanted it. As Administrator, that decision is made by Probate according to who are the closest living relatives.

There was a reason Mom gave you the money. Maybe because you were there for ur parents. In my opinion, anything given before death, has nothing to do with Moms estate after her death. What if Mom had given it to sister before her passing? Different story, huh.
If Mom wrote a will and says nothing about previous money given, and she is leaving the balance of her estate to be split between her two children then thats how its done.

First, if there is a Will being probated, its now public so u can see it. I would ask sister if she has a Short Certificate showing that she is authorized as an Executor or Administrator to handle Moms finances. Probate will tell u who is Executor or Administrator. Give her nothing until u talk to Probate or get a consult from a lawyer. But, I don't think u need to unless...it was a loan.

So she is trying to say that you already have had your share? I don't think she has a legal leg to stand on, the executor's responsibility is to follow the instructions as they are written, not as they personally wish they were written. If this involves a considerable amount of assets then I think you should lawyer up. As a named beneficiary you are entitled to a copy of the will, do you have that?

Assumed executor? Mom would have had to do that selection.

Provide sis a bill on the estate for the care you provided. And make the amount comparable to what is charged through an agency.

You say your sister "acquired" POA in Oct of 2017.   Did your mom give you money before then?   If your mom had not been declared incompetent, she was free to give you money.  Is your sister going to claim you committed financial abuse?  How much money are we talking about?   If you were caring for your mom was it reasonable for care.

Your sister cannot just "assume" sole executorship, but it may be too late to object.