Legal Question in Real Estate Law in California

One owner cannot prevent another owner from use of the home. She either needs to buy you out, or you need to sell the property. You are both responsible for the maintenance whether you live there or not.

You don't exactly sue her for half the house, but you can do something similar. It is called an action for "partition." In the distant past of the law when two people owned a parcel of property and wanted to go their separate ways the actually literally partitioned it, voluntarily or by a court decision. With all the local zoning laws and the Subdivision Map Act, etc., no one partitions a parcel anymore, even if it is vacant land. Instead the court will order a partition by sale, with the proceeds of the sale divided among the owners according to their share of interest in the property. More often than not, however, partition cases settle by one owner buying out the other, or by a voluntary sale and division of proceeds.