My dd6 suffers from anxiety also. It's been diagnosed by a psych and she's had about 20 sessions extending across last year.
Going to school is one of her issues. Her anxiety manifests in pretty bad behaviour. She refused to go to school and it can be quite difficult for dh, myself, and our other 3 dcs.
School are up to speed with this, but she is generally very good at school. Initially, they refused to believe me, but then she started showing this bad behaviour when her routine was changed at school, and their approach to her has improved markedly.
Dd will always struggle to get to school. It's a massive effort to even get her out of bed, let alone dressed, fed, teeth brushed etc, we've tried a number of different tactics with mixed success.
On a particularly bad morning, she will refuse to go into school and cling on to me. Perhaps once a fortnight. In these situations, I have a particular learniñg mentor I look for and they give her a job to do - go to the office, help them do a task, to get her into school.
So, I agree with the above, talk to the school. Hopefully this will really help...