Any class at all could give her two-weapon fighting. It's a feat. Everyone gets feats. Ranger is certainly the most obvious entry into Beast Heart Adept, and she has a ranger-ish feel to her, and there's no particular reason to believe that she's some other base class... but none of that rises to this thread's standards of evidence.

And as for the evidence that her beasts are bonded to her, well, Vaarsuvius follows Roy into combat, and takes complex actions in coordination with his without any verbal commands from him, but that doesn't mean that Roy has a wizard as a class feature. And Greyview assumes that the same sort of relationship exists between Monster-San and Xykon as between Greyview and Oona, and I don't think that anyone assumes that Monster-San is Xykon' familiar.