Legal Question in Family Law in California

You are not quite correct in any of the scenarios. First: she would keep the house but you would not lose your money as long as you document that it is not intended as a gift of your separate property cash. However your money would not buy a share of the appreciation and would not earn interest. You would just get it back in a divorce. Second: Yes, you would keep the house. However, to the extent your earnings during the marriage are used to make mortgage payments there would be a community property interest in the amounts used to pay the principle, and she would be entitled to a 50% credit on that amount. Again, no share of the appreciation or interest would go to her, only 50% of the amount the mortgage was paid down. Third: No. Same rules apply as if you bought it pre-marriage IF you take title as "married man as his sole and separate property" and you document your cash was pre-marriage cash. Same rules apply re: paying the mortgage during the marriage as if you buy before marriage.

All that said, the first option seems least favorable, simply because there doesn't seem to be any benefit to paying down her mortgage. The second and third options are six of one, half dozen the other and just require slightly different documentation to make clear the separate property nature of your funds and where they go to preserve them as a separate asset.