If she had to borrow from a work mate, she'd probably burned all her closer friends and family. Therefore, she's unlikely to be able to pay you back (unless she can rob another Peter to pay Paul).
If you can afford to write this money off, you will have to do that, even if only in your head, since it sounds unlikely she will ever have the money to satisfy all her creditors, even if you do go to court, since council tax and rent and food should always remain her priorities.
By all means take her to the small claims court, though, since it sounds as though she needs to know she can't get away with it.
I know this sounds bitchy, but it might also be an idea to tell others what happened, so no-one else is caught out by her (after all, you offered her money once: she may now be grasping for that kind of solution - robbing Peter to pay Paul, as mentioned above).
By the way, what sanctions were there in the legal agreement you two signed?