all the above +1. There is no room for sentimentality in the property game. Buyer can legally walk away without it costing them a penny right up until exchange of contracts. If she’s mid-divorce I would suspect it almost certainly will not wrap up as quickly as she’s expecting. Estate agents and solicitors will do bugger all to help you out if it gets sticky either.
I can’t imagine she will pay a non-refundable deposit large enough to cover your expenses if you lose the house you want…..
Also, although you could state that a deposit was non-refundable, a wily property lawyer would take all of about 5 minutes to accuse you of non-disclosure of a minor something or other, making the original agreement void.
I know this because my wife’s uncle is one such lawyer who serially makes his wife happy by committing to buy houses, then (when the excitement is over) pulling out at the last minute by citing minor details.