My advice would be a quick call to the mum. Be polite. Check her daughter's OK without saying sorry. If she wants to discuss the details, just tell her the rules of your insurance mean you can't discuss it with her at all; you're sure she'll understand.
Let her know that if she puts details of her complaint in writing you'll pass it onto your insurers and they'll deal with her from then.
Make a note that you contacted her and what was said. Make notes now about what you recall about what's gone on so you're not relying on memory in eighteen months if it's still dragging on.
Then put it aside - it's one of the reasons you pay for insurance, so you don't need to worry about it.
Good luck,
Vin