She was AWESOME
I told her about two hours before we went, phrased like it was suggested here (as a 'pinch') and told her she could show Emmett how to be brave.
When we arrived there was a child screaming blue bloody murder
and we went into the room at the same time as another 4 yo girl and she screamed blue bloody murder as well. I freaked a bit thinking that Cate watching that performance would set her off but she was completely unphased
She didn't even flinch as the needles went in and the second one she even watched going in quite happily...even I am not that nuts as to watch the needle going in!!
I was very proud of her
When we came out into the waiting room, the little girl who had been in at the same time as us cracked it because Cate had been given a sticker and she hadn't...the little girl burst into fresh tears at this realisation...oh God, her poor mother
I am happy I told Cate beforehand so thanks for the advice