*Waves at you
I have in the past have dropped hints to a person who is wearing a strong perfume because they bother me as well. But if they don't take the hint then I get a little more blunt. You can always say something like "That is a really nice scent you're wearing but it is really messing with my allergies. It's making my eyes really itchy, can you please stop wearing it?" That way there is a compliment along with a gentle request. If she refuses to change her scent or stop wearing them, take the complaint to the manager. Because when you say register I am assuming retail or grocery? And if it is bothering you then more then likely it is bothering a consumer with allergies. I know that in the stores that I go to, cashiers no matter what industry are discouraged from using strong scents for that very reason.