If you give her the photos she's either going to (1) give them to someone else to edit (which could go either way in quality), and/or (2) she's going to post them somewhere and badmouth you all over the internet.
Might be time to give her a full refund, and cut ties ... walk away.
Tell her something like "I have done all I can to try to resolve the issue by offering both a free reshoot and/or additional editing, both of which you declined on (this date). As you have indicated that you're unhappy with the work provided and that you are not willing to work with me to rectify the situation, I am providing a full refund."
That way, there's no harm, no foul ... I'm no lawyer, but there shouldn't be any unpleasant recourse from that (after all, it was an engagement shoot which can easily be reshot, not a wedding, which cannot).