My mother has signed the deed to her house over to my sister. Any advice?

My In-Laws did a reverse mortgage and put my husbands sister on the deed. We don't care about the house but it is in SF and they bought it in the 50’s for $20,000.

his parents are now deceased and she is in her late 70’s. We would love for her girls to inherit the house but there is no will and taxes, fees etc will have to be payed.

that is one problem your sister may have, the stepped up basis of the home when adding her to the deed.

the other issue you need to deal with is your Mothers level of dementia when all of this was done. As so many others recommended, an estate or elder care lawyer is a great idea

This is a shame. A real shame because with my siblings, we give full disclosure. I'd find out everything from an Estate Attorney. They can find out who has POA medically and financially. If she does in fact have those things, there's little you can do unless you get your mother to redo and update her current paperwork.

Time to see an elder law attorney. Sorry, but when you get in these legal issues there is no substitute for professional advice.
A Forum of regular folk like us is well and good for the minor questions, but for medical, legal advice you cannot afford to go wrong, which means you MUST pay for good advice.
I wish you the best.

Perhaps your sister is making sure that your mother’s house is exempted should your mother have to apply for admission into a Medicaid nursing facility because of her dementia.

Dementia doesn’t mean mentally incompetent. Only a court can decide that. In some countries, it’s enough for a doctor to say: mentally incompetent (but this can be appealed).

She could have mild dementia and still be legally allowed to sign. Even though she later forgot, it can be allowed. As long as the person is able to retain information long enough, understand the consequences, etc., they can be allowed to sign. It all depends on the extent of dementia.