Have her plant leaf lettuce fairly heavily in the shape of the first letter of her name.
Show her how to 'snap' a snapdragon.
Tell her flower 'stories' -- here's a link to some, I'm sure there are tons more, but keep them very very simple.
http://digital.library.upenn.e...
Teach her simple names of flowers and praise her when she can find/identify.
Press flowers.
Pull apart a pansy to show her the lady with her feet in the bathtub.
Radishes are an extremely early and reliable crop, try the Easter Egg mix.
Dip edible flowers in egg white then sugar and let dry - borage is easy for little fingers to manage.
I agree with the glove suggestion, and also small tools. If you can swing a tiny wheelbarrow, kids love to push those around. Or a wagon.
Easiest of all, just let her tag along with whatever you are doing and chat her up along the way.
My granddaughter used to help me garden, and I got a laugh out of her delight when she proudly pointed out the first 'bloody heart' one year.
