I don't know about her, but one way you can change colors is by going to image > adjustments > replace color. Once the replace color box pops up, you select the areas you want to replace the colors of and you can adjust it by hue, saturation, and lightness. Make sure you're working on the right layer though.
the layer that is going to be used to shade set it to multiply and clipping group. you can find these settings right above your layer area in sai (hope you figure it out ^_^) if not I can help you figure it out