Is it possible to reverse a ruling of mental impairment?

I think you'd have a hard time proving that.

What do you mean by psychiatric abuse, and whom do you suspect of wishing to induce memory loss in the elder in question?

Give more history of the situation.

A person who is an elder, living in Independent Living, who has a judge rule mental impairment is not likely to be living independently. Is this the person you are caring for? Seems to me vulnerable person could get better-is this what is happening?
Can you be more specific? What is your relationship to the abused?
How is person being protected from abuse at this time? Where did the abuse occur? Was there a criminal case?

If the person is better, have the senior start seeing a forensic psychiatrist regularly. This doctor can testify to the persons true mental state, over a period of time.

My advice is usually: "What can be done with paper (judges ruling) can be undone with more paper".

Why do you want to do this, since clearly it is a vulnerable elderly adult, at what age? When last I checked, how sane or competent does one have to be to achieve your goals for this person?

Hoping you get the answers you need and want, and that I did not scare you away with all those questions. Just think about the questions, no need to answer to me.

But maybe someone can help you with more information.