Dana finds herself caught in the middle of the relationship between Rufus and Alice. Why does Dana use Rufus to get to Alice? Does Alice use Dana?
I understand what this question is asking, but I would definitely hesitate to say that Rufus and Alice have a relationship that Dana gets in the middle of. I would hesitate to say that for two reasons.
First, I wouldn't say that Dana finds herself caught in the middle of the relationship. Dana is very responsible for the relationship existing in the first place. There wouldn't have been a relationship without Dana encouraging Alice to stop fending off Rufus's advances. Second, I hesitate to call what Rufus and Alice have as a "relationship" in the traditional boy/girl/man/woman/love sense of the word. Alice is "with" Rufus to protect herself. She can go along with his advances and sexual demands, or she can be beaten and raped.
Dana's decision to convince Alice to have a "relationship" with and have sex with Rufus is entirely a selfish decision. Despite the fact that Dana lives in 1976 and has never see Back to the Future, she adheres to the movie's time travelling logic. Dana knows that her family line comes from Alice and Rufus. She believes that if Alice and Rufus do not produce children, Dana's family lines will cease to exist. Therefore, Dana would cease to exist. The logic makes sense as long as only one timeline exists and changes to the past can influence a future. This is why Dana uses both Rufus and Alice. Dana needs both of them to survive and produce children in order to ensure her own future existence.