As much as I like Juvia (especially with the new hair style she abandoned), she's not a hugely impressive fighter. She relies on the few water attacks and the limited invulnerability but once those are proven ineffective, I don't think she has what it takes to overcome the hurdle.
If you consider her character, all she ever wanted were friends that would accept her and now later a man that would sweep her off her feet. When did she ever desire to become a strong kickass fighting machine? From what I could deduce, she only became one of Phantom Lord's elite because she was so disappointed in her life and the people around her.