Will she be sent to different places? Yes, it is the military. Will she have a say? Yes but at the end of the day you go where you are sent.
But the choices are effectively trades group limited. Some trades group go to many places and some go to very few. From the postings here it would appear that TG12 has a very limited mobility. If she doesn't like Northumberland then Lincolnshire it is.
Once she has a tour under her belt I am sure other positions will become available. Unless it has changed there are a few ASOP at Waddington. It is that first tour which is important. Learn the ropes, don't act bored, and keep smiling.