In what township are you?

In most townships (though this does vary), the lease is in fact void without a valid COC.

If you have not already done so, file it. I don't think it will make the current lease valid, so you will likely be best off if you simply accept her desire to terminate, and hold her responsible for the damages. Due to the lack of a valid COC, it's doubtful that a claim for the unpaid rent would hold up in court, but the damages should if it becomes necessary to drag her to small claims court.