Fat quarters are a good start as there are suggestions at patterns for things to make on Pinterest.
A pair of good quality fabric scissors would be good, with a reminder never to use them on paper.
Decent cotton is a must, cheap thread will break on the machine.
Some bead topped pins are useful, also some embellishments, such as ribbon, flowers, motifs or buttons, to add interest to her makes. Perhaps some wadding to stuff animals, hearts etc.
All these should be cheaply available on line on eBay.
You could cut up old cotton sheets, curtains etc. For practice pieces. I hope she has fun, my GDs love sewing.