She finally managed to stop being a wimp and kokuhaku.
Just by itself it is a noun, in the sense:
He was completely surprised and rendered utterly speechless by her kokuhaku.
So there is your lesson for the day. What does it mean? Well honestly I thought I knew but it turns out that maybe, just maybe I don't afterall. We'll see. That's the fun thing about the Japanese language (and life in general), there is always a new surprise waiting to be learnt.