How do you "just find out" that your insurance is canceled?
This gets mentioned often on YA, but I have yet to hear a reason as to how it suddenly expired, without the car owner knowing about it. Even if they cancel it on you, they have to send you some type of notice.
If it expired, you had the expiration date somewhere. You either chose to ignore it.....or chose to not renew your insurance.
Also, even if she files it under her insurance, she can go after you for the damage. If she has to pay, she can make you pay.
I'd give her a call, and just find out how much the damage is, and take care of it.