It is completely legal for the lady to have the guns deactivated. However they should to be surrendered to a Section 5 dealer (or the police could take custody, pending deactivation) until this occurs. Your firearms department should be able to give you a list of local ones. He/she could probably deactivate it to proof house standards and have it proofed. Any competent gunsmith will know how but they must be S5 registered to undertake the work.
However, I believe they are still technically S5 until the proof house has inspected and approved the deactivation. In other words, how do you get them to Birmingham?
I got a (.357 Magnum) Heritage pistol returned from Belgium and all was hunky dory until I arrived at the UK port, when I had to arrange a S5 dealer to transport me to Bisley. However, he was excellent about it, charging only £60 for the day's work.
Section 5 carriers (different from S5 dealers) charge an absolute fortune (I was quoted £2 per km from one carrier for a 450 km journey).
I once tried to describe our firearms laws to a Dane, after several minutes of mirth his comment was "Your politicians are equally stupid as ours".
Sums it up in a nutshell.