This will end with either a FULL return (shirt plus bag), OR she gets offered X amount of posh credits and she accepts (you get your money and posh pays her to keep), or posh will refund her and release money to you and just call it null and void. She will keep items in this scenario. I have never seen a return request rejected. She has probably already stained your item or took pictures to make it look like it did, so posh will side with her. Mostly, they're trying to avoid her doing a chargeback. Anyway, if she does return just the shirt back to you, make sure you have video of you opening it, and showing contents. If she purchased these items as a bundle, they must go back as a bundle.
I had a claim against me rejected. The person said the item was not as described because it didn't fit her. I don't replied that that the item was a size small as listed. It probably didn't fit her but that was not my fault. He claim was denied.