She is suing you for damage you state that your son caused. Why do you think you don't owe for damage your son caused?
Did you have an agreement pertaining to utilities? Was there a period of time when you were splitting the bills, or regularly making a contribution?
The ad on craigslist was posted before or after the drawer broke? If it was before, and she sues you in small claims court, present it to the court when you argue that her claim is too high.

