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If you both signed the lease, then you are both responsible for the entire rent to the landlord under the legal doctrine of "joint and several liability". So you are liable for the entire rent and she is responsible for the entire rent.
If you had a private agreement between the two of you to split the rent, then you can sue her for half the rental payment in small claims court if you both agreed to break the lease. Then you can garnish her wages, seize any bank accounts, and levy on personal property to collect on your judgment..