She is the lessee and SHE will be in breach of contract and she may be sued by the LL and you!
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If you both are on the lease, you are both equally responsible for the entire amount. So that means if she does not pay, you are responsible for the amount and then you can sue her for her portion. With it only being another month though, it is probably easiest (and cheapest) to just pay the rent yourself and not worry about it.