Singing assemblies

I'm looking for advice for my 8yo daughter.

She is currently on the ASD pathway, and really struggles with singing and 'calming' music. She has been allowed to stay out of singing assemblies for over a year, but school have now implemented singing into every assembly. School are insisting that she needs to go into these assemblies as "In life things will happen that she needs to get used to"....

She becomes instantly distressed with these songs, and will sit with her in-ear plugs in, and her hands on her ears and cry throughout the whole singing part. As she has no formal diagnosis yet, I'm struggling to get the SENCO on board to keep her out of these assemblies, or to allow her to leave when songs start.

Any advice on my next steps?

Thanks in advance!