Legal Question in Real Estate Law in California

First, land is not lost to adverse possession so long as the owner of record pays all the property taxes. So, your mother very likely still has a viable claim to the two-foot strip. Further, this is not a situation where the neighbor is likely to be able to claim a prescriptive easement.

However, a document described only as a "site plan" doesn't sound like convincing evidence of where a boundary is located. Site plans are prepared for many purposes, and not all of the possible purposes demand that it be, or be based upon, an accurate survey by a licensed surveyor.

So, the bottom line is that your mother can probably bring a successful action in ? El Dorado County Superior Court to quiet title to the two-foot strip and perhaps also to allow her to move the fence or to require the neighbor to move the fence. In order to succeed, she will need a recent survey by a licensed surveyor showing the relationship between the fence and the true property line. The site plan you mention may not be recent enough or reliable enough for the purpose.

I have other easement and boundary cases in the Placerville and Forest Hills area and could efficiently represent your mother if the family decides to attempt to quiet title and/or get the fence moved as a trespass.