Hi Wayne, yes trying to be reasonable with them may not work. Remember that there valuation would include sending one of there contractors to go and buy one, fetch the keys, put it in the property ,and return the keys. Most of the contractors will have a min call out of 80 ish quid. Plus they may bung up to 20% on for themselves.
That's how they would get to this figure. If she disputes it,it will go to a tenant dispute panel, which takes 90days. She won't get a penny of her deposit back until they judge whether the deduction to her deposit is reasonable.
Sorry for the bad news.
Jen