People can get allergy to sunlight. It is called photosensitivity or sun allergy. The most common form of this is known as polymorphic light eruption (PMLE), also known as sun poisoning[1,2]. This is characterized by redness of the skin found on the arms, wrists, neck, and other areas. Here is a picture of this:
Based on your description, this is what is going on. Your friend has mild PMLE. Pheromones have nothing to do with this problem at all.
How does this happen? Scientists aren't fully sure. However, what we do know based on our knowledge of allergies is that the sun-exposed skin. The sun must be altering the skin in some way.
How does this have to do with eosinophilia? Well, eosinophilia means there is more eosinophils and eosinophils are responsible for allergies, so there will be more allergic reactions to more things. However, eosinophilia and photo-sensitivity both are symptoms of drug allergy. Perhaps your friend is allergic to some drug. For example, I found that eosinophilia and photosensitivity could be an allergy to Lisinopril. I am not sure about the drug history of your friend so I cannot say anything more but she should go to the doctor for sure.
Mayo Clinic - http://www.mayoclinic.org/diseases-conditions/sun-allergy/basics/symptoms/con-20035077
Drugs.com - http://www.drugs.com/health-guide/sun-allergy-photosensitivity.html
Patient.info - http://patient.info/health/drug-allergy-leaflet
MHRA UK Public Assesment Report (UKPAR) for Lisinopril - http://www.mhra.gov.uk/home/groups/par/documents/websiteresources/con054513.pdf