Christmas cactus? Herbs from seed you could use for cooking.

Get her the supplies and help her make a terrarium. All you would need is the soil, gravel, charcoal, a large jar and any decorative items. Then go shopping together for a few plants.

The large amaryllis bulbs you see in the store now are fun.

I don't know how old your child is, but kids like to chop the top off carrots, sit the piece in water and watch it re-sprout.

You sound like a very loving mom. Lucky child.

Nasturtiums are good you can eat them too

For indoors spider plants are good starter plants for young ones. they can take a good bit of neglect and still rebound once they get water again. they don't require much work and readily adapt to various light levels. Once the plant sends out runners the kids get excited to see the baby they planted off of one has now grown and sent out its own runner(s)

BIG smile sunflowers are great indoors it is what my children started with and now my girls are putting up lattice in their room to grow climbing sheel vine and my son has bird of paradise growing in his room Marigolds grow good indoors also

Try this...

Here is a link that might be useful: CG online-gardening with kids

Do you have a balcony? If you do, you might takes a good look at the balcony gardening forum, you'd be amazed at what people can grow out there!

Here is a link that might be useful: Balcony Gardeing at Garden Web

Again depending on the age of your child...
I saw a cute project
Supplies:
Window box
Soil
Glass beads (like for a fish tank) or pea stone
radish seeds

Fill box with soil as you would for any planting, then with the seeds- write your childs name or initials, cover lightly with soil, then cover with thin layer of rocks or glass, careful not to disturb the seeds.
Radishes work well because they grow fast. They will not mature enough to eat, but just pull them when they go by and write something else.