My 12 year old daughter has SPD

My daughter is 12 and had SPD sensory processing difficulties!! And we have just started the autism  assessment. she’s at high school year 8 we have lots of concerns but one main one at the moment is underwear I can not get her to wear underwear, this is very upsetting as she has started her period as well and won’t wear knickers has anyone come across this situation and what things have you tried to help overcome this problem 

karen x