She is a shaper who specializes in shaping plants, giving them extraordinary side affects.
On their way to battle Carnag, the group stops at Gerta's house for help. She welcomes them into her house, and provides them with vegetables and fruits that she grew with shaping. When eaten, they give the consumer special abilities that only last for a certain amount of time. For examples, her carrots allow the consumer to have night vision for hours, and other vegetables make someone feel like they've eaten three days' worth of meals despite only eating one.
She also provides insight on what exactly Carnag is for Mira.