I wanted to answer before, but my son is so much older than your daughter.
DS2 with high functioning autism started biting his nails later, around 5 I think. I deregistered him from school aged 10 due to overwhelming distress and have been home educating in an autonomous way ever since (because it suits him). Last summer, after 2 1/2 years of de-escalating situations, doing lots of accepting, living a much, much less stressful life, he happened to stop biting his nails and skin. It was gradual, a longer nail here and there, then the nails became dirtier (due to not being in mouth). No more plasters on his red, hard, raw, sore thumbs.
Instead of telling him not to bite his nails and being cross, I'd be on his side and ask if they were sore and gently hold or kiss his hands. I also told my mother in law, lives next door, not to be verbally aggressive about it to him, that was hard to do.
Interestingly last summer he restarted being interested in reading for his own pleasure again, it had been knocked comprehensively by school. So a new love might have shifted something in him at a deep level, something which I couldn't have planned or directed. My own nail biting went away of its own accord the very day I started working on a till for the first time in my life, so that's why I suspect there is a link for him too.
I hope this helps.