The only trike I've ridden had a coaster brake. No feet being thrown off, at all, you just turn it backward a bit to stop.

I'm sure insuring bicycles or tricycles is much cheaper than insuring automobiles (and actually not required, by law, as it is with autos). I would think the rider would be responsible for damages, and not the owner of the vehicle, but that's just a guess.

Regardless, somehow bicycle rental businesses manage to exist in every major city. So, it must be possible to insure them. I would think the personal injury risk to her customers would be the bigger insurance concern, but if I were doing it, I'd require customers to sign a very strongly worded waiver of liability for injury.