Will the airlines accept an expired license as ID?

To try and make it as smooth as possible, I would check with TSA and with the airline she will be using. Not sure where you are but in NJ motor vehicles facilities are open with restrictions (some are doing licenses only others are doing registrations). My license was due to expire 10/30 and believe me I dreaded going to the facility (wait lines are been pretty long) but when I went online to see where I would have to go, there was a lovely little covid 19 msg that said normal renewals could be done online. WOO HOO!! If she is giving up her license (and if her dementia is increasing rapidly, you really don't want her to drive) check with your Motor Vehicles facilities and see if she can switch to a non-driver's state ID online .
Good luck!

I don’t think so unless your DMV’s are still not fully open. Ours are now open but there can only be a certain number of people inside you sign and get in line. Everyone else has to wait in line outside the building and until their name is called.

My mother-in-law left my father's funeral and went to the airport without her purse, so she had no ID of any kind. They were going to let her on the plane (LA -->San Francisco), so it's not unheard of to get on a plane with no ID, let alone a recently expired DL.

I would not allow her to travel if she has any Dementia.

They accepted mine, but I don't recommend. One time I showed, during height of my bro's issues, flying from San Francisco to Palm Springs, with a license from 2003. Don't ask. Long story on this mistake. The agent said "You are giving me a license from 2003???? I nearly fainted. Now I had purchased my ticket with card in my name, had one other picture ID and several other ID (nurse license, what have you). I had to go through pretty thorough search; in fact they used it to teach another agent what to look for. I got through. That said, this could go either way and I don't recommend. She should go to DMV and apply for Senior ID, relinquish her license; they will punch it, give her the paperwork. She has no passport I am assuming. I will never know if I got by because flying within state or not. I got home easily as well, as they had the records of how I flew there. But what a terror. My stomach dropped right out. You mother should wear good N95 mask. She should call airline and see what they suggest.

Here's what Google says on the subject:

"The Transportation Security Administration (TSA) is relaxing it's traveler identification rules in light of the impact of COVID-19. TSA will accept expired driver's licenses or state-issued ID a year after expiration or 60 days after the duration of the emergency, whichever is longer.” Mar 24, 2020

I would call the airline directly to be sure, if it were me.

Good luck! I hope she has no issues with her ID or with her flight in general.