Translation:She likes to smoke after drinking alcohol.
The most common structures that use 在 to express before/after/during an action (V) are:
在V前 = 在V之前 = 在V以前 = before V (V can be a verb or a noun)
在V后 = 在V之后 = 在V以后 = after V (V can be a verb or a noun)
在V时 = 在V的时候 = while V (V must be a verb, e.g. 在开会时 = while attending a meeting. To say "during N" where N is a noun, use 在N期间, e.g. 在会议期间)
I'm pretty sure that the full form of these structures (with 在) can be used in all circumstances, so keep 在 if you want to be on the safe side.
But 在 is probably optional. In fact, I am yet to come up with an example where 在 cannot be omitted.