If you want that type of extensive analysis your best bet is to consult a local lawyer.
Ordinarily, a person who seeks to recover rent owed by an ex-roommate for the duration of a lease has a duty to mitigate (in essence, that means "minimize") damages. Usually, that means that if a suitable alternative roommate can be found, they can only collect (a) rent for the period before the roommate moves in, and (b) the (reasonable) difference in rent between what the breaching roommate was obligated to pay and what the new roommate pays over the duration of the lease.
In your situation, you seem to be offering your girlfriend the option of walking away and owing nothing. If she is willing to make that same offer to you, and your landlord is willing to release you from the lease, you have already indicated that you would accept that result. If not, you move out, and she attempts to sue you, you may be able to use your offer to evidence that she did not seek to mitigate her damages. (I've not encountered this exact situation, and certainly not under your state's laws; I can only speak hypothetically, and a judge could reject this type of defense. A local lawyer should be able to give you advice you can rely upon.)

