Any idea what's causing DD16's rash? (Pic included)

[YodellingForJesus]

She was at a friend's house last night. She noticed a few red spots appearing on both hands and wrists, then within an hour they were covered with this rash. The rash has gone down now, and she feels fine, but she says it's happened before when she got scratched by our cat. Don't know if this is coincidental aor not. Her friend has cats too, although neither of them scratched her.

She has mild allergies (to some fruits) and hayfever, so I am presuming it's connected to that. I've never seen her react that badly though, should we be worried?

PS The red mark round her wrist is from her hair elastic

[AllIWant85]

Definitely looks like a reaction to something, I get a similar rash if I come into contact with some cleaning products.