Extremely Severe Sun Allergies

My wife has severe sun allergies.  If she is exposed to strong sunlight for even a short duration, she will develop raised bumpy rashes in the exposed areas, with the worst at the neck, hands, upper chest, and legs.  Her discomfort and itching can last up to a week after the exposure.  She has allergic reactions to all and any sunblocks that she has used to date, even those prescribed by her dermatologist.  When she was young she never had this sun allergy, but it seems to have stemmed from a day at a water park, where her parents continued to lather her with a variety of sunblocks and bug sprays.  Could it be that those chemicals, along with those in the pool water could have changed her skin's chemistry?  

Is there anything that we could do or try?  Any cures out there?  

Thank you for any and all help!


Sincerely,

Ben