Unexpected Shot Today

I'm not a happy camper today. We dropped off Reese's health form to our pedi's office Monday so they can fill out her shot record. They faxed it to her little school and I get a call late yesterday evening that shes missing the chicken pox shot. I assumed it was a mistake on the pedi's part so I call them and sure enough the nurse tells me she never had it. She said they "FORGOT" to give it to her. How do you forget? I'm going to have to take her and Saige in the RAIN to go get a stupid shot. I still don't understand why the chicken pox shot is something they "need" anyway. Poor Reese :(