If your medicine isn't working, I would get rechecked by your doctor or something, see what can be done. I know I was surprised when I tried various OTC allergy meds (did not like Zyrtec) that they each had different pros/cons for me. I knew to check different ones though because my prescription thyroid pill, the different inert ingredients in each labs batch, I responded differently to each of them. The active ingredient in each of the allergy meds is different, maybe Zyrtec's doesn't work as well for you as another might?

Yeah, having to talk about sensitive subjects in the workplace is very hard. I remember a story my stepmother told me where she got elected to tell another woman in the office she needed to bathe more, that she did not smell good!

Hmm, if I were your over-scented woman, I guess I would prefer to hear it from another woman; have you any friendly women you do work for that you trust and might approach, talk it over with them, try to get them to broach the subject someway (as if coming from them instead of you :-) or who could give you tips on how to approach her yourself? If it were me trying to approach someone, I guess I would try for humor and making it as much my "fault" as possible; that I have a problem, not that she wears too much or too powerful a scent. But that might not work because she might not get it and would leave it up to you to solve your own problem. Too, it's not like if she has too much on or the "wrong" scent that she can instantly fix that? I'd definitely try different meds, see if I could find something that worked better, try mouth breathing as much as I could around her, keep my office door mostly closed and get a cheap desktop air purifier or something; I'd go so far as to get the label of being "too sensitive" and then others might be more careful and you could then bring it up that "perfume" (not just hers, every woman's) brothers you and you wish "women" would not wear so much sometimes. She might get the hint.