Definition of "grown up"

Today is our first, official snow emergency, so Gwenchik stayed home. At some point, after we exhausted all the puzzled and board games, she wanted to watch the movie Madeline.
Gwen: Mom, Madeline is small, but all grown up.
Me: How is that?
Gwen: She is small in size, but already managed to get into a lot of trouble all by herself--which makes her really grown up!