Is the monthly fee still around $850 and covered by Medicare?

Medicare does not cover assisted living. The amount you quoted sounds way too low for assisted living, or even basic rent in Orange County. Where did you find that information?

4 years ago in Atascadero at California Manor

It was probably an income based Section 8 housing. Assisted living for years later in a different county in California? Does she have Medi. Cal? It would not have been paid by Medicare but might have been subsidized by a Medicaid waiver.