Well.....just something you might think about first.....what happens to this house in their divorce? If it's community property, she might be forced to sell it in the divorce. In that case I doubt a lease-to-own would be acceptable. Her ex could force an immediate sale to get his share of the equity. You need to find out a lot more about the possible outcomes. Also.....homeownership is not a panacea. Repairs and home maintenance are expensive. How old is the roof?
These are all good observations - bottom line I think is do your due diligence before you leap, but on the surface it looks like a good opportunity. Well worth checking in to.