The flower might grow in an unexpected way or have some magical transformation. Maybe it starts to talk or show special powers.
Well, it could be that the flower becomes very friendly with the little girl or that it starts behaving like a human. Maybe it even leads the little girl on some adventures.
Possibly, the flower could reject the human food and teach the little girl a lesson about what's right for different living things. Or, it could grow so big that it causes trouble for the little girl and she has to find a way to fix it.