Besides the basic notions, I would suggest you precut fabric and some hexagons for a Grandmother's Flower garden. This pattern is very easy and you would have a high chance of success for her to make a small doll sized quilt pretty quickly. It also has the advantage of being portable so she could bring it to family events for some one-on-one time with Grandma.
My second suggestion is to NOT use a traditonal sewing basket and use a Caboodle instead. If sewing is just a fling, she can still use it for other hobbies, jewelry or, when she's older, makeup.
Most of all, have fun!