This is such a complicated issue that you should let your friend to consult an attorney. Additionally, without knowing which state your friend is in, it is extremely difficult to answer this question. I wrote a general article based on California on the issue. Your friend can search on avvo to find it.
Generally speaking, according to California law, a court will use Moore-Marsden calculation to calculate how much asset the community will get and how much the hu*****and will get as his separate property. Since the hu*****and paid the down payment before marriage, the house would be his separate property. But there are so many other issues to consider. First, is there a pre-nup? Second, how they pay the mortgage debts? Thirds, did they refinance and if so, how is the title written? Fourth, is there any post-nup? Fifth, is there any other declaration that can be viewed as transmutation? Without knowing such details, nobody can answer your question.
