Seem like it should be: She returns to our stage to appear in "The study in Terror" by Lucille Fletcher. This sounds like the person is an actor, acting in a play called "The study of Terror" for a theatre troupe. 這個句子讀起來就像她是戲班子裡的一個演員

David is right. This sentence is said from the point of view of a theater that is introducing an upcoming play [舞台剧]. It speaks of an actress ("she") who is coming back to that theater to perform in a play called "A Study in Terror" [恐惧的研究], by Lucille Fletcher. That play is about Sherlock Holmes [福尔摩斯] and Jack the Ripper [开膛手杰克]. You could translate the sentence as "她［某个女演员］回到我们的舞台，将出现在Lucille Fletcher的A Study in Terror".

The girl returns to the class and she fells terrified by Lucille Fletcher