I tried to respond yesterday but my iPad flipped out and deleted my nearly-finished response, and it was a long one. I'm gonna try again, and it's long, but I think it may help since I was a situation that wasn't exactly the same, but the solution may translate.
I'm a special education teacher. One of my students last year was a lovely girl with a very demanding mother who was very much a bully. My colleagues told me she's been this way with every other teacher that has had her child.
Basically, everything it did wasn't right to her. The work I gave her kid was way too challenging, and then it was way too easy. I was sending home too much stuff, then it wasn't sending enough. She complained to anyone who would listen that her daughter was regressing in my class, her performance was worse since I'd been there (lies. We tested her several times with several tests, she was actually improving).
She would tell the principals that her daughter came home crying over how mean I was, how mean other students were, and how I let it happen. She said I would punish her daughter for no reason. Again, all lies. When interviewed by the guidance councellors, principals, other teachers, etc, the student never once said anything that her mother was claiming, she actually love my class.
She wrote aggressive emails and notes to me demanding explanations for everything, cutting down my teaching ability, basically being a bully. She sent these emails and notes to other parents as we'll.
I know this is long, bear with me, I totally have a point, I promise.
My bosses and several other parents had witnessed this behavior with other teachers, and assured me she did this before, and I was not the problem. So, here was how I got her to finally lay off:
I killed her with kindness. I was always nice, smiling pleasantly and speaking calmly when I saw her in person. In notes and emails ( of which I made copies and cc'd to my bosses, as teachers we must always cover our asses) I was sickeningly sweet and saccharine. I was always chirpy and cheerful with her, when she would have a brutally worded complaint, my response was "thanks for the info! I'm glad you told me. I appreciate it when parents communicate their concerns, it helps me improve my class and my ability to teach your child!"
Of course, once I was with my TAs or with friends, I vented like crazy, I just never let her see me mad.
This sounds like absolute bullshit. But it works. It pissed her off to no end that she could not get a rise or negative response from me!
I think OW may be trying to do the same thing: bully you and get a rise out of you. Show her it won't work, and she'll get bored and stop. Also, let your boss know just in case she tries to tell them something. Mine understood and it never affected my job, they knew she was lying and just trying to start stuff.
A positive: it will make her SO mad when her silly little scheme won't work :)