Are you sure it's BOTH the flu and Chicken Pox? Fever, headache, feeling generally yucky are symptoms of both, and although flu usually gives you a higher fever and potentially a more severe headache, there are other diseases that can have similar symptoms but be more dangerous.
I found that for my kids a homeopathic combination that I got at my local health food store helped tremendously for both of them. (by day two they were both feeling much better even though they were at different disease stages).
For us, oatmeal wrapped in a bag/cloth with a rubber band tied around it soaked in warm water and dabbed gently on the spots in the bath helped some also. (I also squeezed it out into the bathwater for more soothing effect)
Baking soda mixed with warm water and dabbed on the pox sometimes helped the itch too.
What are the other symptoms? Chicken pox can rarely cause other problems so I'm sure you know to see the doctor if you have a high fever with vomiting, severe headache.. etc.
I hope she feels better soon!