She said she just does not like doing things alone as it just makes her anxious and she doesn't know why.
It's probably because these skills need to be scaffolded and learnt in stages to build confidence.
I can also understand her fears about it escalating tbh.
Re supermarkets. When my children were young, they would accompany me shopping so they saw the process (I'm sure yours have done the.same). But that is not enough to learn.
We progressed to going in a couple of times where I'd stand at the till with her and talked her through what she needed to do (either manned or self service) just buying a couple of things that she (not me) needed/wanted.
Then I'd stand back and let her do it herself and just offer reassurance or answer questions she had.
Then I'd stay in the car whilst she went in on her own but I was always outside.
Then she walked down on her own.
Life skills need to he taught and scaffolded to increase independence and confidence in doing them.
If she had reached 18 or 20 without ever having been taught, she would be older and possibly feel more confident anyway. Her thought processes would he different but, at 14, she is just a child and needs to be taught.