Here are the threads listed on her web site in the supply list for the class we watched online.
___The Bottom Line,Bobbinfil, Tru-Sew, Metrolene, Sew-Bob, Clotilde or YLI Bobbin & Lingerie. These are very fine, synthetic threads for the bobbin.
___30 or 40 wt decorative threads in colors that contrast with your fabrics. Can also use variegated. These can be silk, rayon, acrylic or polyester.
I just Googled "what thread does Libby Lehman use".