PD, I have an allergy to most chemical sunscreens. Noone else in my family has this. It took me along time to figure this out and back when I was a teenager there were few options. I would break out in a small red itchy blister type rash. It would show up 12 to 24 hours after I had used the sunscreen and last about a week or so. VERY FRUSTRATING and miserable.
I have since seen two dematologists about this. One told me that I was probably mildly allergic to the sun and the chemicals enhanced this condition. Any way, your grandaughter needs to stay aways from ALL sunscreens except those with titanium dioxide and/or zinc oxide (these are physical blockers) as their active ingrediants. Don't be swayed by labels that claim the sunscreen is for babies, sensitive skin, or mild as water, etc. READ the lingrediant list.
These are some examples of sunscreens that will work:
Neutrogena Sensitive Skin Sunblock Lotion SPF30
Blue Lizard Australian Suncream - Sensitive SPF30
Blue Lizard Australian Suncream - Baby SPF30
The Blue Lizard is more waterproof than the others. Also, beware that anyone wearing regular sunscreen should not pickup or hold your granddaughter as the regular sunscreen will rub off on her. (I have the opposite problem; my 2 year old gets regular sunscreen on me!)
I hope this helps.