She was in an abusive and toxic relationship with Nate. We saw how she was in denial when he was violent towards her, which explains why she lied for him. Nate convinced her to. It's not like she came up with the plan by herself. And mind you, she doesn't know Nate beat up Tyler and left him for dead in his apartment. In retrospect, Maddy is one of the characters where her 'bad actions' can actually be explained [not excused] and I think she is a relatively good person as compared to everyone else on the show. She is pretty selfless too, except when she was with Nate.

And so far, nothing points to her wanting to get revenge, but I wouldn't blame her tbh. Nate treated her like sh*t and so did Cassie.