Whatever you have time to show her, most of it will stick! I can remember tending potted plants with my Mom at that age, separating zinna seeds from chaff at my Aunt's house, picking veggies for dinner in Gramma's garden. Why we don't teach all elementary age kids this stuff is a serious mystery to me. Everyone should know where their food comes from!
Butterflies were mentioned above, which which I agree very much! Watching a caterpillar turn into a butterfly is very powerful and fascinating to folks of all ages.
Have a blast!
