Is autism an acceptable reason for authorised absence

Our 15 year old daughter has had a diagnosis of autism for a year following several years of issues, including school refusal. 

After the first few days of absence, the school has started marking her absence as "unauthorised", even though nothing had changed. As a result, we are now in the council led disciplinary route (even though they don't call it that)  with threats of fines etc, In our first meeting, the EWO explicitly stated that autism is not an excuse for non-attendance. 

Is there any point in pushing back on her absence being classed as "unauthorised". From what I understand, unauthorised means the school believes there are no valid reasons for her absence. The school has otherwise been understanding but don't know if it would be a waste of breath pushing back on their absence classification (as that would remove the threat of fine and jail).

 Help!