I have a slight sensitivity to scent as well which I find gets worse the more I am exposed to scents (which could explain why her's is worse). Also, the winter can be worse for people with this sensitivity just for reasons like the windows always being closed etc. I think you just need to do as Lee Bee and others suggest. Tell her you will not use the scents on the days their child is in daycare and if their sensitivity is still triggered you would understand them needing to find alternative care. I also don't use scents around children for the above mentioned reasons.