Quick question - how does she interact with the other roommate? ie is the other roommate having the same problems with this person that you are, or did she define boundaries that she is respecting?

You do not want or need to be her therapist, especially unpaid, and I don't think she has asked you to be.

Can you call a roommates meeting to discuss rules / air grievances?

Remember that this is YOUR life, your graduate study experience, your future being affected; don't let her, anyone or anything take it away from you.