It is California and they do have domestic partnership laws.
She can try to sue, but only for the last 6 months.
If all the major property is in your parents name, she does not have much of a case.
If you can prove that each of you paid 1/2 of the bills while she was there, then she should only be allowed to take what is hers.
But, do be aware that there are some slime ball lawyers there that just might take her case, so just be prepared. She should loose, but you never know. (She was just paying rent with benefits)