If you translate it word by word, I mean, grammatically, "我去" mean "I will go". But we usually don't say that if we want to go, we would say "好吧！","行啊！" and the like. On the other hand, "我去" is buzzword in internet, which means "Oh, My God!" "Holly Crap!" or the like. It is used when you feel surprised or when you are in a bad mood. The word is dialect of North China.

It depends on her tones. If she says it as usual, she will go. However, if she says it in stress on the first word"我", she won't go. It's just represent a feeling, like 哦，哎呀. more similar with f*ck or sh*t,but not so strong. If you familiar with somebody, you may use this and means no offend.

we must hear the voice of Xiao hong, otherwise, we cant say whether she goes or not.

小红goes for 夜宵。 我去means：I will go(with you)

小红没有去。