A lot of people use silk thread as it is so fine ( 60 or 80 or 100 wt) that it just melts into the fabric and becomes invisible, which you want when doing needle turn applique. I don't like it only because it tangles on me. I know that the way to avoid that is to use a length no more than 18 inches long. I prefer to use 60 wt. mettler cotton embroidery thread. It also becomes invisible when the stitch is done correctly. Take her up on her offer to teach you and do as she suggests. Once you learn the technique, if you are not happy with the materials that she suggested, then you can experiment on your own. I simply love needle turn applique and have taught many others to love it too.