M.B.
Have them done one at a time or two but NOT all at once.
Ask for novicain instead of laughing gas. In my opinion, gas doesn't work as good. I wouldn't give her that.
Keep her home from school.
Be in there for her to be reassured and hold her hand.
Probably will be advised not to eat right after so eat before and brush. Then afterward take her to McDonald's for a chocolate shake (or other flavor) or frozen yogurt then ask doctor when she WILL be able to eat.
Start w/soft foods: spaghetti, soup etc.