This is aninvoluntary and uncontrollable physiological response. If you're outside on a bright sunnyday, it may be difficult for even your magnificence to dilate her pupils. Similarly, ifyou're together in a dimly lit room, her pupils are probably going to be dilated no matterhow much she despises you. One other thing to keep in mind is her base level, or natural pupil size. This variessomewhat from person to person.
Some people have larger pupils and some have smallerpupils.
Please try to be inconspicuous about this. Do NOT tell her what you're doing. If she hadany idea it would make her very uncomfortable. She can see it inyour eyes. And, short of wearing sunglasses or avoiding all eye contact, there's not muchyou can do about it.