indeed and teenagers her age are well known for their stubborness, the more you take something away from them forcefully the more they want it so blocking access may not be the best course of action as it might just make the problem worst. The way I see it is at the end of the day she has to make a choice by herself and the best way for a you to help beat the addiction is by getting her off the game by non forceful methods.
*If the worst come to the worst you can aways resort to mental warfare and tell her she sucks, her class sucks, her class is going to be nerfed by blizzard, she will never get into a good guild, pvp sucks, wow has no end game etc etc.
*(Not recommended)