What you all seem to be forgetting is that it's against eBays rules & regs to threaten/extort negative feedback...
I.E., it's a reportable offense.
I'd report her so fast her head would be spinning. She might not be aware of the ruling and you can notify her that it is most definitely a reportable offense and she will be reported if she doesn't keep her communication in a business like manner. (still report her just let her think your not reporting her just warning her)
Daayyyummm newbies. Gotta wonder if she's done this before under another ID.
Do zactly what Jeri/Signsintime states about letting her know you took the time to see that she won an identical pair. Once "outed" she may back off thinking she has the upper hand.