Taxes on property are owed by the owner of the property - so if your sister is being sued, the county must still believe she's the owner of the property. However, if there's a lawsuit, you should be able to get the information about the suit and who's representing her from the clerk of the court (often this is available online). Check there to get the details of representation.
Evan A. Nielsen is licensed to practice law in California and handles federal tax matters throughout the U.S. The information provided here is for educational purposes only and is not intended as legal advice for a particular matter. This response does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult an attorney.