Feeling like a bit of a failure

My 12 year old daughter was diagnosed as autistic in March, which was both completely expected and a total shock at the same time.  After the diagnosis we had a feedback meeting with CAMHS as the assessment had been done by an external partner company and we were discharged from them as they felt her school would be able to support her and that if we need them again we can always contact them.  The problem I have is that she is really struggling and it is a massive battle everyday to get her to school.  She doesn’t know what it is exactly about school that makes her not want to go.....she has intervention sessions at school with an ASD teaching assistant and 3 other students and is allowed to leave school 5 minutes early so she can leave when it’s quiet.  They are pretty good at making sure her needs are met but she just doesn’t want to go and everyday starts with a mini-meltdown.  

I usually work and don’t get home until 6pm but after several instances of my daughter ringing me in tears as she’s not coping for various reason and me feeling like a failure of a parent for not being there I have been signed off sick from work as everything has just really got to me now.  I did speak to my work in March about the possibility of flexible working, explaining about her diagnosis and how she is struggling now she is in High School and was told by HR that they would speak with my management but nothing has happened since.  I am struggling to work out what the best course of action is....obviously she comes first but I am a single parent and have rent/bills that have to be paid.  Does anyone know if I can request reduced hours at work due to my daughter needing me home?  

Thank you for any advice!