@UnderTheNameOfSanders you said you weren't sure what kind of help you need - I think either an "educational psychologist" or a "clinical psychologist" (both protected titles, both requiring doctorate level training to qualify) would be able to help your dd with strategies and advice in a holistic way. You could research local practises and talk to their practice managers, or talk to bps.org.uk about how to find someone suitable.
I think based on what you have said I would say aim to get her back to school and doing the same GCSEs as originally determined - ie helping her cope. I think that the best way to do that is by helping her talk about everything, all her thoughts and feelings and worries, exploring everything, maybe getting her to write things down, and you helping her with coping strategies for each specific concern and empathy and support.
I am not sure homeschooling is an option if you struggled to get her to work/teach her during lockdown. A 1:1 tutor might be an answer to helpwith academic things but this might exacerbate any feeling of being "different" and not help with social aspects
Crowds - has she or can she explain if this is to do with feeling self conscious, being adopted, being bullied, wearing masks, being different, feeling stupid, others wearing masks, virus fears... and so on... it could be to do with any number of things for her and each specific concern might have different strategies or remedies that would help her overcome
Plan for weekends, making sure she is doing things she likes/which are good for her, like sport if she does sport, spending quality time with you if that makes her happy, etc
If you spoke to a clinical psychologist i think that you could also get help with tips and strategies to help you help bothof your dds build autonomy and confidence going forward.