<<<but it must be horrendous when you know there is nothing wrong with you but you cannot formulate your words.<<<
There must be brain damage not showing up on the scan. Does she have difficulty in pronouncing her words (aphasia) or when asked to name an object e.g a cup, she cannot think of a name, but knows what to do with it (nominal aphasia).
It is not acceptable that she has been thrown on the "NHS scrapheap)...insist that you want her to be seen by a speech therapist (if there is one in your area)