Benefits are for people who need them because they don't have enough money to live on. They are a vital safety net and I'd like to kneecap the bastards who are trying to take them away from people who need them 
However - If someone's circumstances change and they have enough money to live on - benefits should stop.
I think that's only fair, really.
So if the inheritance is large enough that she loses benefits - she doesn't need benefits, iyswim. They're for people who need them in the here and now, not for people who used to need them but have now come into some money. If you have your own money - that's what you're supposed to use to live on!
I think you can have is it £8000 in savings before they start reducing your benefits? Or certain benefits?
I think that you can use a sum of money to do certain things, but I am not an expert - I am pulling this out of the back of my head where I think I remember reading something about it! But can't you pay of debts or stuff like that? Something that is about improving your situation, and if that uses up the money, then so be it?
I think what you can't do - legally, or bloody morally! is buy yourself a flashy car and a big tv and bugger off to disney world and then come back and say please can I have my benefits, the money is all gone.
She should get some financial advice.