Firmly, but carefully clamping the vial with her beak, so as not to break it; Mary pushed off the stopper with her tongue, tilted her head back and let the contents flow onto her tongue. Dropping the vial back into Amy's hand, she braces herself as her changes begin.
Mary's whole body begins to shrink as her talons morph back into hands and her claws retract into fingernails. Fur and feathers shrink away as her beak forms back into her proper nose and jaw while her wings shrivel and vanish. Her belly develops the proper curves and... bulges of a slim young woman. Her tail retreats as her hindquarters revert to human legs.
Mary discovers something's off when she stands up to find herself the same height as Amy, and getting smaller. As she continues shrinking, Mary feels her ears grow longer and sharper. Flower petals began sprouting all over her body, firmly wrapping themselves around her, forming a beautiful gown. Two large flower buds grew out of Mary's back and unfolded into the shape of wings.
"Cool, Mara; you're a pretty flower fairy!" Amy squealed.
"It's Mary, actually." She corrected the little girl in a tiny voice.
"Sorry, Mary. That's a prettier name anyway." Amy smiled.