Why is 在 in 就这样在孔琳犹豫不决地跟着朋友进了酒吧?
I think your teacher meant to say: 就这样，孔琳在犹豫不决之间跟着朋友进了酒吧。Because 犹豫+地 doesn't sound good (Surprise! You cannot add 的/地 to any word to form an adj/adv)

犹豫

v.迟疑不决

他犹豫着要不要跟着朋友进去。

a.迟疑不决的，缺乏主见的

他平时就是个犹豫的人，此时自然指望不了他来做主。

If you search 犹豫地, most likely you get 毫不犹豫地 instead of 犹豫地. Because 犹豫 is the state that one cannot make decision on whether or not to do something, you shouldn't use it to modify "do something". If you want to express the idea of "weighing for a long time but finally do something", you can say: 

volunteering:

他犹豫再三，还是跟着朋友进了酒吧。

by force:

他在犹豫之间被朋友拉进了酒吧。