[US] Question regarding death and power of attorney

I have a client whose brother in law died, normally this would not be an issue however her sister (married to the BIL) is in a coma for almost 2 years now.

The issue is he was taking care of their medical expenses but now he is no longer with us what will she need to bring in order to take control of the funds for her sister and her BIL's funeral.

I'm at:

1: death certificate 2: any judge ruling or PoA 3.???

Normally ID ask my manager or back office but the former is busy the latter is unhelpful. Any assistance would be appreciated.

Edit: autocorrect ducks