Legal Question in Real Estate Law in California

Not if they have a deed that show she only owns a 1% interest.

Not very likely she has a valid claim to half, but until the actual numbers regarding contributions to the ownership of the house are sorted out, there is no way to say exactly what her share is worth.

I must disagree with Mr. Roach and perhaps with Mr. McCormick.

The ownership may be quite different than shown in the recorded deed. Under a principle called "purchase-money resulting trust," equitable title to real property often follows contribution to the down-payment.

If it can be established that the ex girlfriend paid one-half of the down-payment, and didn't intend to make a gift of 49% of the property to the ex boyfriend, she could prevail in an action to quiet title to a 50% interest.

Indeed, if she paid 100% of the down-payment, she could prevail in an action to obtain full ownership -- or 5%, or whatever portion of the down-payment she made.

When there is a solid case for a purchase-money resulting trust, it doesn't matter what the deed or the public records show. After a successful trial, the records can be modified by court order.