What you should have done:

Reported your car stolen to your insurance company. According to you, the mother already called the police and the son admitted it. So you would have had a police report to furnish your insurance with. Depending on your policy, all the costs of the damage could have been covered and you would not have been out of pocket, apart from losing some of your no claims bonus possibly.

What you still can do:

1.Give the woman an extension to pay the damages.

2.Press charges if she wont pay or fails to pay by that date.

3.Name and shame on E-I.
(The loss of business she could suffer as a result of not paying for the damages her son caused could far outway those damages).

4.Come to an alternative arrangement between yourselves were she makes up for the damages in a different, non financial manner.