I'm betting that she was too cheap to pay for a reserve and the dress didn't sell for enough money.
I'm guessing that you're unable to leave feedback because it was canceled before you had a chance to pay. Had you paid and got a refund, you could have left feedback.
I'd still call ebay, suggest that this seems to be a case of a no-reserve listing not going high enough and the seller cancelling. As further evidence, point out that the relisted item is a fixed price listing.
The least they should do is put a note on her account that she's not completing no-reserve transactions.
I bet you wished you'd paid immediately so you could have left feedback!