It sounds to me like your seller had the automatic-feature turned on for Open an Unpaid Item case.
What she should have done was start a seller-imitated cancel for being Out of Stock and take the defect she gets for that.
It's possible your seller is either very unskilled at this ebay thing, or craftily trying to avoid getting into trouble.
I hope all this communication between you is in ebay Messages because I think you're going to have to call ebay Customer Service about it.
It's too complicated for suggesting easy solutions.
Calling Customer Service can be an exercise in frustration but, in light of what you have said, I think this is the only way you will be able to avoid an Unpaid Item Strike on your account.
You'll find the number to call under Help and Contact at the top and bottom of the page.