these are a big AIT provider there are lots of others though, so worth just googling AIT, UK and autism.
If she's not ready to hear anything it's difficult to say very much. You could try "I was talking to somone who said that her child was very sound sensisitive and she found that AIT really helped him" It doesn't have to accompany autism, but when she starts searching she'll find a lot out there realted to autism- you don't have to mention that though iyswim, just stick to sound sensitivity (especially if someone just "told" you iyswim).