Rob - You may want to do some reading about internet addiction, other compulsive behaviors like gambling addiction and shopping addiction, and obsessive-compulsive disorder. Some of these are successfully treated with medications like Prozac (I have a daughter with anorexia/bulimia/OCD who reponded well to high-dose Prozac).
Enabling the behavior surely doesn't help it, but you may want to find out more info before deciding on the best intervention. Does she have family or friends who would be likely to help you with an intervention?
