Complex sentence: She is being pressured by Dominique, a girl who claims to be a vampire, to do something that the reader never finds out, and when Morgan does not give her an answer, her acquaintances start dying mysteriously.
Split into simpler sentences: She is being pressured by Dominique, a girl who claims to be a vampire, to do something unspecified that the reader never finds out. When Morgan does not give Dominique an answer, her acquaintances start dying mysteriously.