Later start to school day

Hi all. First post. After some advice please.

My daughter was diagnosed in year 8, she's now in year 11. She's always struggled with senior school, and had to move in year 10 due to bullying and lack of support. She even tried to take an overdose last year so her mental health is my top priority.

No echp as last school was not supportive of it but new school have started the forms. Her new school is much better at the pastoral side of things and adjustments but her attendance hasn't been great to date and we have dealt with school refusal but she tries her best and has gone into year 11 with a fresh outlook and a lot more positive. However school starts at 8.30 and whilst school have agreed she can come in by 9 when registration closes, problem is I can't get her in before about 9.15-9.30. it just doesn't happen.. she needs time in morning and wants to get quieter bus (school is 3 miles away). School have told me it will go as unauthorised absence and I could get a fine etc from local authority.

I realise this is an important year with GCSEs but i see the fact that she is in school at all a huge bonus as just getting her there is an achievement. What can I do to prevent a fine or escalation? Would an EHCP help? 

I appreciate all these rules are coming from the local authority not necessarily the school as such, just grateful to know where I stand.

Thanks in advance