What a nightmare story. Sounds like this whole family were very badly let down with the mother and daughter both having learning difficulties. Then the GP deregistering her. Unbelievable.
I know a family where the son has LD and will only eat bread and potatoes. Never eats fruit, veg or anything else. He just point blank refuses everything else.
My own daughter was prescribed some mild antidepressants about 3 years ago and has never taken one yet. We encourage, we bribe, we discuss and we do our best but she just will not take them. They are supposed to help with her anxiety and low mood.
We had a few children at school who ate a very limited diet or hardly anything at all. It was very hard to get professional help.
I researched how to tackle this and support families as part of my course at Uni. Until I did my research - I didn’t even know it had a name - ARFID. The school paediatrician and dietician never gave it a diagnosis - giving it a name would have helped school staff and taken away the guilt some parents felt - as it is a recognised condition.