Try researching "photosensitivity" in children.
Your daughter mainly got affected in the areas that are more hit directly by the sun- face & back.
Photosensitivity can bring on symptoms like your 15 month old has. Here is a link:
http://www.wrongdiagnosis.com/p/photosensitivity/signs.htm
http://my.clevelandclinic.org/disorders/sunburn/hic_sunbu...
Keep in mind, that even in the "shade" people/children can get affected by the sun or burned. This is "reflective" heat or the sun that reflects off of surfaces etc. We don't "see" UVA or UVB rays... but it's there and I've seen people even get burned on rainy & cloudy days. Some skin types are just more sensitive. People can even get "sun poisoning." My father had this once after a day out fishing. He ended up in the hospital later that day.
In addition to sunscreen, (and if your child is sensitive to creams & things on her skin)- a great thing is to have your child wear SPF protective clothing in the sun. You can find it at Amazon.com Just type in the search word "SPF clothing for children" and many choices will come up. Land's End also has these type of clothing. Here is the link:
http://www.landsend.com/ix/index.html?store=le&action...
In Hawaii, where we live, most children here use these types of clothing, and adults too. It is a highly recommended item to get and wear.
Take her to the Pediatrician, especially if she seems uncomfortable.
Take care,
~Susan