My roommate moved out early, am I now liable for entire rent?

At the risk of being blasphemous, God doesn't trump contract law--and a lease is a contract. She may not simply ignore the lease and her obligations thereunder.

However, note that if the two of you were on the lease, the landlord has the right to expect full  payment of the rent. If not, the landlord may evict you. So you need to make sure the landlord receives the full rent; then you in turn may sue your former roommate, if necessary, to recover her share.