This is the best one i could find with pictures.You have to scroll down a ways to get to the place where they show you how to do it.HTH
Kathi

http://www.sewusa.com/Threading_Diagrams/Threading_Pages/Singer_Sewing_Machine_Threading/singer_640_threading_diagram.htm

You could try a sewing machine store - see if they will show her how to do it if she brings in the machine.

So did you get it figured out????
Kathi

I have this machine. to wind a bobbin, place the bobbin in the case, close the bobbin door all the way and then pull it back open just about 1/2 way until it clicks. Thread the needle, and hold onto the thread tightly and press on the foot plate as if to sew. The bobbin will begin winding thread on it. The thread in your hand will cut off od the bobbin by itself f you pull on it gently after winding the bobbin quite a ways. When it gets to the blue line on the bobbin, you can stop there and shut the plate over the bobbin. No need to cut the thread if you don't want to, you can just put the material in and start to sew. Hope this helps. You can contact me if you have any more questions at lawillie@yahoo.com

The last answer sounds correct except on my old touch and sew I had to turn the hand wheel on the right side of machine, backwards so it would disengage the needle so it would stay down.