Legal Question in Real Estate Law in California

A proper answer will require additional information:

First, a "mobile home" can be either real estate or a motor vehicle for legal purposes. You asked under the "real estate and real property" heading, but unless the mobile home has become immobilized, it may still be a vehicle. Very different registration and recording laws apply.

Next, although you had an oral agreement regarding payment, what written evidence of the transaction(s) might exist? Was there a transfer of title at the DMV? A recorded deed at the county? A rental agreement change at a mobile home park? Any e-mails between your sister and you regarding negotiating the deal? Any letters? Canceled checks? Anything that tends to show a deal between the two of you would be helpful in overcoming the so-called "statute of frauds" which requires certain dollar-amount transactions to be in writing.

A final set of questions an attorney should ask you would involve your relationship with your sister and her ability to pay or to respond in damages if you sued and won. Many lawyers are hesitant to recommend lawsuits between neighbors or family members.