Be sure to include hemming; repairing a seam; sewing on buttons, snaps and hooks and eyes; making a dart; putting in a zipper (those new lace zippers are darling!); pressing vs. ironing; and using a commercial (McCalls'/Simplicity/Burda) pattern. Most of those are things they will wish they had experienced, at some point in their future.

Jan in VA

Wow, so many ideas!! I can't wait to get started with our lessons. She's coming over today and we're going to start with some simple hand sewing and sewing on buttons. I'm thinking she would love to make some pajama bottoms and I've pulled a few of my commercial patterns to teach her to learn to use. We'll start with Simplicity and work our way up to Burda and Vogue.

I would do a mix of hand sewing and machine sewing from the start. Build on each skill.
There is no certain age - it has more to do with hand-eye-coordination. I've been working with two DGDs with very low HEC.

I'd really like to so these in units. Perhaps do a unit on applique. Another on garment sewing (a much longer unit, obviously). Any thoughts on different units?

I think a lot of it has to do with the student's interests, abilities and time.

Sounds like you have a great list of projects. Zippers and buttonholes are ones you might add. A reuseable shopping bag/tote might be useful to her. Potholders would be an easy quilting project with a useful product result.