Marigolds are easy, but the little girl might not like the smell. Also, if they planted a succulent, she could learn about different plants' water needs.

She may still be able to find some spring bulbs (tulips, dafodils, etc). My first year with a balcony, I planted bulbs quite densly in large (plastic) pots, let them collect snow over the winter, watered when they were dry (I was in Albuquerque that year, very dry in winter), and was rewarded with lots of flowers in the spring. But they need to be planted soon, as those bulbs need a chilling period.

I also have planters with violets and pansies in them in the spring. My kids have a Pooh book where Pooh and his friends plant little gardens and Piglet grows pink pansies. My DD (age 4 now) insisted on having pink pansies last spring. Unfortunately, our planters are out in front of our house, and deer wander through the yard and eat pansies like candy. I planted them 3 times before they lasted more than a couple of days.

Good luck to your friend and her daughter

Catherine