I feel like I should make a big, dramatic showy entrance for the amount of research done in fifteen minutes to make sure I didn't tell you the wrong info. So... 'toon me up and throw in some science or something!

Hot water is your friend. If you want to straighten her hair, get some boiling water and either pour it over her hair (carefully, so as not to burn you! and I also like to avoid the face as much as possible) or dunk her hair into the water. Brush til it's stick straight (or else it'll kink again). Let dry. Rejoice! This is also how you curl their hair (only obviously with that you'll need to curl their hair around something, usually straws) and there's a cool down period on that one. (Instead of brushing, dunk their hair in ice water to set it.)