Why is 在 used in this sentence?
Why is there 在 "她喜欢在喝酒后抽烟。"?
喝酒 = is drinking
In this case, the 在 expresses the "when" of "smoking" and is a set with 后 to mean after; it does not express present progressive but rather sets up the circumstance under which "She likes to smoke".
"在......后": after (doing) ___
"在喝酒(之)后": after drinking
"她喜欢在喝酒后抽烟。": She likes to smoke after drinking/She likes to smoke after she drinks.
“She likes to be doing this before she does that.” This sentence generally means “she likes to smoke before she drinks”. In Chinese, the 在 gives the meaning that she wants to smoke before she drinks, and therefore stands as a “be” in a sentence. Does all that make sense??