>>43547257She can act in the way you prefer, she knows you as much as you do, maybe you don't know, but she will find the way to make you happy, because, she likes more than anything, to see you happy... and memories exist for a reason, don't be afraid to change, probably what you want is as you said it Childish, playful and sassy, and a gardevoir could be that...
Just know, because the norm says that they are gentle and elegant, doesn't mean there couldn't be one that breaks the norm.