My Daughter, 46, Has Many Allergies Causing Sneezing, Watery Eyes,

My daughter, 46, has many allergies causing sneezing, watery eyes, nasal dripping etc. takes otc Zyrtec, Benadryl, Claritin. Recently if she has an itch and scratches it, even lightly, she gets baseball size hives where she touches or scratches her skin. Happens on shoulders, arms, face. What's happening and is it dangerous?