You say it's an encroachment on your freedom but wouldn't asking her to stop wearing it be an encroachment on hers? Just something to think about. There's no good direct way of telling her but if its really bothering you I would maybe send out a company email stating some updates on policy or reminders about correct uniform including the overuse of personal products like makeup or perfume. If that doesn't work maybe hold a brief staff meeting to say that your allergies are getting worse and that whoevers wearing a lot of perfume needs to use a bit less.

I'm autistic and very sensitive to smells but I wear perfume because its comforting and helps me to feel less anxious when out and about - maybe she has similar reasons? I hope you manage to sort this situation out for the best.