I'm a bit late to the party but essentially, she grew stronger to a point where, when facing the Trix and remembering all that Valtor did since she met him and what he did to her planet, her rage alone and her pure will summoned and allowed her to get the enchantix fairy form, to evolve. Her will to save everyone was enough to cheat the transformation and actually trick it. But only when she actually did save her planet did her transformation become complete.
