Unfortunately most of us will have this happen at some point, most guys hearing a lady bad mouthing another lady will think she's an idiot and ignore, they don't want to hear it or get involved. I doubt it will really effect your business, it will probably damage hers instead. Is it really effecting your business, I say that as virtually no one who books me via AW leaves me feedback, probably as I never ask for it, but are you seeing your numbers down since she has started this.
Just put somewhere on your AW profile that you don't offer bareback and get regular tests done, and ignore her, she will eventually give up. If you start an argument with someone like this it never ends well, and just makes things worse. I think ladies doing this are quiet, not doing the money they want, and basically just jealous.