Is her hair curly? You didn't really say. K has wavy hair and can curl if done correctly and can be dried straight. We bought the sponge rollers at Wal-Mart in the hair accessory area in Health and Beauty. There are a variety of colors int he zipper bag. We found the green size is perfect for K's hair. She looks like Shirley Temple when we take her hair down and brush it a bit.
We wash k's hair with regular shampoo and then take sections of her hair and roll it up on the sponge rollers. Not dripping but definantly very damp. If it's too dry it won't hold the curl. I let K sit under the hood style hair dryer for about 30 minutes on low to medium heat and then sleep on the sponge rollers. In the morning we take them out and finger brush it or brush the curls where I want them. After an hour or so the curls are lengthening and looking more like a natural curl instead of a poodle...LOL. I don't add any products to the hair at any point, it tends to make the hair sticky and not natural looking.
K's hair will stay looking curly for about 4 days with each day the curl relaxing a bit more, but her hair has some natural curl to it to begin with.
Braids make wavy hair, not curls.
If you wanted to bypass the sponge rollers for a temporary curl that will be gone after a few hours then buy a good brand of heat activated hair spray, lightly spray the dry section, then use a small-medium sized curling iron on tiny sections of her her to form the curls. My beautician says the "heat activated" is the most important part of what I just typed. If the hair spray is NOT a heat activated one then it makes no difference and the hair won't stay curled for more than a few minutes and will fall flat. The hairspray will weight it down and it will not work.
Practice will make it easier for you. I practiced about 4 times before I figured out how I wanted to do her hair for a Shirley Temple number that her dance class did this past May. You'll do just fine and find what works for you and her.