Mom's reverse mortgage is paying for her care. How do I handle this while I am obtaining guardianship?

ID - where is your mom?
If she’s still in her home & getting in-home care, then RM isn’t a problem. As long as RM required things are done - pay property taxes & homeowners insurance, do maintenance - she’s in compliance with the terms of the RM. They don’t need to know her status.
BUT
if she’s moved out of her home & now a full time permanent resident in a NH, she’s out of compliance for the RM. RMs allow you to leave the home for a while - like do a long cruise or several weeks visit to kids - but you have to return and it’s still your full-time residence. If not, then the RM will call in the loan as you've defaulted on mortgage agreement. Property taxes payment status is online and that seems to be what often triggers a compliance audit. Some RM have contractors who do routine drive by’s on properties to see if maintained & look occupied.

Find her RM paperwork as it will detail what causes her RM to be out of compliance & the timeframe to let them know. Look to see if penalty for drawing funds once moved out of the house. I’m with GuestShoppe that if you draw on any RM funds and mom has moved into a NH, this could be a problem for you. It could totally derail you being appointed guardian as you didn’t show fiduciary responsibility. Instead judge will likely appoint outside non-family guardian from a list of vetted by the courts guardians.

Guardianship filing has costs. Maybe 5-8k. Do you have the $ to do this? Not mom’s $ but your $? If you become guardian, then you can use her $ (if she has any) to repay those costs but you still have to front $ to do guardianship as you really need an attorney. Personally I wouldn’t count on getting any $ at all from the sale of her home for mom to have as an asset to pay for care as RM has interest and fees atop the loan borrowed that has to be repaid and usually way way over the value of the home.

You mention she has had 24/7 care for 8 years now. There’s no DPOA? In the 8 years of her on 24/7 care, how banking, other financials, property management & medical stuff been handled? Whose been signing off on things fir her & in what capacity?

For now I would wait. You DO need an attorney and do ask. I will tell you that now, today, before you do see someone, do not make a move. Many reverse mortgages USED TO HAVE clauses which said that the loan had to be repaid after the senior was out of the house for "more than yea many days"--whatever amount of time it stipulated. This meant that many seniors, with hospitalization and rehab, were forced to sell their homes to repay these loans. I have heard recently that there are many good reforms in reverse mortgages, BUT, if you have access to her contract get someone in the know and read it carefully. You need to be very careful about things that can bite you big time. See a laywer. It is well worth an hour of his or her time to protect you and your Mom now.

Generally to obtain guardianship you will have an attorney and your mother will be assigned a different attorney, You should ask either or both of them your question of when to inform the reverse mortgage lender. But, to answer your immediate question, I don't think it's your place to inform the lender of anything until after you become your mother's guardian and/or conservator. Best wishes during this hard time.

Do you have legal standing to notify them without guardianship? Is the bank likely to trigger default on reverse mortgage and seek immediate settlement? Read papers carefully so you don’t cause problems with that while you seek guardianship. Especially if you need to continue to draw funds for care pending final settlement. Also what Barb said. Attorney familiar with elder care and Medicaid.

Have you retained, on your mom's behalf, an eldercare attorney?

I would do nothing until you have sought legal advice.

Likely, the time for moving any funds was 5 years ago, before the "lookback" period. Moving anything without legal advice is fraught with issues.

Do not commingle any funds.