Fairenuff - she is really a confident person, so I am not worried about her coming out her room or making friends. She is very sociable, ran loads of groups/societies at school, can talk to large audiences without any prompt; has interviewed lots of famous people for her newspaper etc. She is the sort who will go and knock on other people's doors to get them to come out. Her anxiety is in complete contradiction to the rest of her character but is easily traceable back to an illness she had in Y11 when she kept feeling dizzy and nauseous. Your dd and her flatmates sound lovely and caring!
bigbluebus - dd successfully avoided her triggers through most of sixth form by just not going to assembly and all her teachers knew that she could just get up and walk out of a lesson if she needed to but her counsellor said that that was the worst thing as she needs to expose herself repeatedly to the situations she is scared of until she sees that she can cope. Unfortunately counselling started after she finished school. She has had an email back from the college counsellor already who has seemed lovely and arranged to see her, which I think will give her a safety net. You are right that you do need to face your own situation sooner or later in order to fully get better but I know from watching dd struggle that that is easier said than done 
sassy - how cosy. I love the college parent system - it does make you feel that they have someone to call on and to show them the ropes. Dd has subject parents as well (2nd years) and she has a meal out planned with them and all the subject children as well as meals with her college family.