I had a similar experience and had to get 2 door skins and the swine drove away, the bodyshop made a good job of it and i dont notice it. Gutted for you. Sometimes the culprits move after the offence, did her door have white paint? If it did or even if it looked liked they had wiped it off I would have seaked recompense either the hard way or easy.
I dont condone violence but sometimes its the only message some people understand.