How do I get rid of squatters

What is the name of your state?California. My mother (currently 80 year of age), inherited her deceased mothers home in northern California around 1988. This property has been vacant for several years. I recently went to see the property. Not to my surprise there was a squatter living on the property. I identified myself and asked her how long she had been living there and she said about three years. Apparently, she had water and electric turned on. I know for a fact, this person does not have permission to live there. Although that is not her claim. No type of rental agreement has been established.

After bringing this information to my mother, I immediately checked the tax status. I found the taxes have been delinquent for five years with the exception of one installment back in 2000. After speaking to the assessor, they advise us to bring the pay the current taxes and make arrangements to pay up the back taxes. That is exactly what we did. The 04-05 taxes are paid.

Given this information, what are my mother's rights as the property owner? I most likely will have the power of attorney to act on her behalf.
1. Can she be sued for back rent since she gave me an estimated date of possession?
2. If she has made improvements to the property, can we be sued for reimbursement?
3. What evidence do I need to take to the authorities to prove ownership?

Please advise

Tell them to move...get the sheriff

Tell them to move, in writing, if they dont get the sheriff. I doubt a squatter will sue, it takes Money to sue. Secure the property.