Does your vet know what food she is on? I would be surprised if he knows the recommended amounts for every food so it sounds like he may have picked a figure out of thin air!
If you are mixing wet and dry I think it is quite important to weigh it, especially if both are complete foods. It is easy to accidentally over feed when combining. Forthglade make two versions, one is complete and one is intended as a complimentary wet mixer so it might be worth trying that one if you aren't already.
I don't know about the dry Wainwrights but I feed the wet trays and they changed their recommended amounts last year. They almost doubled them.
I stuck to what I was feeding with no ill effects. Archie is just under 17kg and only has two thirds of a tray a day. It looks very little but it is good quality food so less is needed. He also has quite a few treats and a chew in the evening.
You could also look at lower fat versions of the wet food. Forthglade do a lower fat fish variety, Wainwrights also have a lite version and fishmongers trays are also very low fat. If I think Archie is looking a little round I give him those two or three times a week for a while!
