That's because of the time spent in Edolas, the ensuing Tenrou Island debacle, and then her own laziness. From what I gathered, Take-Over requires being "close" enough to what-ever takes them over.



Mira was possessed by a demon as a young child, Elfman was bit by a large lizard, while Lisanna has been attacked by several animals. If she went out of her way to get bitten and/or attacked by more animals, she'd get more animal forms.



Pecked at by a raven? Take over Raven soul. Mauled by a bear? Take over bear soul and so-on.