Gosh, yes, well she certainly ought to wait for the roof, doors and kitchen to be replaced, I would think. What would that lot cost? £15-20K?? Complete guess on my part.
She could buy her house after this work is done, hang on in there for five more years (taking her to her early seventies) then sell and have not only the sale price of the house but also the remainder of her lump sum to buy somewhere else that is more elderly-adapted.
But what does she actually want to do? Does she really acknowledge that she has choices now, or does she feel obliged to commit to this house forever, what with it being your Dad's lifelong home?
She could buy a holiday caravan/lodge, or a campervan, or pool her money with one of her DCs & have a granny annex alongside their house, go on a world cruise, blahdiblah.
Does she feel that she must do something very sensible with this worryingly large sum of money asap?
Waiting a few more months might be wise, as you've said too.