@HippyHoppy
Heirhunters is back on, in the mornings so, if you are thinking about this in terms of what she might inherit, I think that, if he dies before you and he made no will, you get the lot. But, if you like her lots, she gets nothing, if you died without a will since, by then, she's only an in-law and the automatic rules pass everything to offspring or other next of kin, as set out in the rules (which I cannot describe in detail, not having read them myself).
Basically, if you want any control, make a will. Yes, it will cost but consider it as a big gift, for them to remember you by.