First, introduce her to the machine and all the working parts. Teach her what the hand wheel can do, proper way to load the bobbin, how to take the bobbin and bobbin case out and look inside the lower end for fluff, how to tell the front from the back of the needle ... and why they are shaped the way they are, what the tensioner does ... and doesn't do if the presser foot isn't down, show her how the feed dogs move, show her just a few different presser feet and why they are different and what they may be used for, and of course how to wind a bobbin and thread the machine.
Start by having her run the machine without a needle - but with fabric (so she can see/feel the speed). She'll get a good feel for the machine/foot pedal without the fear of "ruining" any fabric and no fear of injury by the needle. It's kind of like driving a car ... when I taught my son how to drive this summer I had him press the gas with the car in park so he could hear/feel the engine rev to know how far to depress the gas. When someone presses the foot pedal for the first time they may freak themselves out if they press it too far down before they're really ready to go.
Fabric ... grain. LOF, WOF and bias. Show her and have her stretch some scrap pieces and tell you which is which. Tell her where we prefer to use LOF, where LOF or WOF doesn't matter, and how to handle pieces where using the bias is unavoidable. If you have them, and are using them ... the difference between certain fabrics (printed quilting cotton, solids, batiks, home spuns, flannels ... etc).
The importance of prepping fabric. Are you a pre-washer? Discuss why, or why not - give her both sides of the coin and let her make an informed decision. Ditto for the starch discussion. Also in the prepping area ... ironing the yardage ... iron with the LOF.
Rotary cutters are SHARP, and the ruler needs to be held firmly in place with fingers out of harms way. I would start her on smaller pieces with smaller rulers (perhaps a 9.5" square) so she can get the feel by planting her entire palm on the ruler to hold it in place. She can work up to the longer narrow ruler that requires changing the position of the hand to make the complete cut.
Make sure she makes at least one mistake sewing so you can introduce her to the seam ripper
This way she'll know that if she makes a mistake sewing ... all is not lost!
Straight seams makes the whole job easier. Teach her how to make the seam a consistent size. If pinning the fabric, teach her the proper way to pin so she doesn't hit pins when sewing, and doesn't skew the fabric in the pinning process.
Pressing seams is just as important as sewing the seam straight. Teach her to set the seam first, then press. Discuss pressing to one side vs pressing open.
Most important ... have fun!!