Thanks, I just found this on Essex Police website but it doesn't cite where it's from:
The law states:
Even if there was no personal injury involved, if someone holds you
responsible for the accident they have the right to request your insurance
details. This request can be made later and not necessarily at the time of
the accident. A failure to provide that information without a reasonable
excuse is also an offence.
It will also be a condition of your insurance policy that you report the
accident to your insurance company within a reasonable time, even if you
do not want to claim yourself. A failure to do so can give your insurance
company the right to refuse to cover you in the future.
So that makes me hopeful. I think it's time to write her a letter, I'd just like to know the law so I can cite it.