The more you cry, the harder she will try

 

To feel the power, a big part of the allure.

Over the dinner table, you can ask her: Feel satisfied now?  who else was there? who will you be telling to when you get back to school? ...  Not rhetorical questions.  Show genuine interest.

Most of the bad things we fear do not materialize.  But we fear anyway.  Fear is a big motivator.  In case something goes wrong, we can tell ourselves that we feared, thus we are blameless.  The biggest among all fears is to be blamed.

Don't take her behavior too seriously (at least not appear to be.)  Emphasize to her that you love and care about her and want to see her happy.  If she is unhappy, remind her that she is 20 years old, if she is unhappy now, when is she going to be happy? when she is like you now with job, kids, house to take care of and bills to pay?

Her unhappiness will not save the world, her happiness might help a little. She wants to save the world? Start with herself.  If she cannot be happy herself, how can she save anybody else's happiness?