AFAIK, 12.2 is the only currently valid software that can be installed onto it.
A restore won't revert your software.
Just let her run...hopefully it gets better. If not, then try a wipe and restore and set up as new.
FWIW, I wish that Apple would let us revert to older versions of software. I understand their reasoning for not allowing it, but that doesn't mean that I agree with it.