Yes you both can sue her for contribution.
That is basically how its done.
An action for contribution works akin to a contract action.
1. There is a contract.
2. The parties are jointly and severally liable on contract K.
3. Each party owes contribution under contract K to the full amount of the lease payment per month.
4. Parties A and B paid, and party C didn't pay.
5. Parties A and B are owed contribution, equally for what C didn't pay up through termination of lease before it becomes a month-to-month.
6. Damages are $X to A and B jointly or A so much and B so much.
After lease termination, the month-to-month is A and B's sole responsibility as either A, B or C could walk away at the end of lease.
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Yes, if she broke the lease she may be liable for the damages. Is there a provision in the lease about penalties for breaking the lease? If not, she should be on the hook to both of you for her share of the rent (and any damages she may have caused) for the balance of the lease term BUT only if you have used reasonable and continuing efforts to bring a new roommate in but have been unable to do so. If you do not try to minimize your damages, it will likely be found to be your loss and not hers. Good luck.
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