Yes, Jamie is correct. In a community property state, such as California, he might be entitled to half the proceeds, with exceptions, for example, she inherited the house. I would, if I were in your position, advise her to retain legal counsel ASAP.
The big question is did your soon to be ex father in law financially support the house? My experience/knowledge is that even if you inherit a home if your spouse financially helps you maintain it it becomes community property and they have a claim in it. Hope that's not the case here.