I know that most people don't understand the difference between a seamstress and a quilter. I can and do make and repair clothes and such but I much prefer piecing a quilt. My friends have no problem asking me to sew for them, whether it is new curtains or a seat cushion. They don't value my quilting, they value my sewing skills.
As to your situation, I don't know what I would do. You offered to teach her how to hem and she didn't want to. She was smart enough to know that there was a product out there that could be used instead of sewing. I probably would have done the same thing (given her the coupon) but I would have told her what to get and then offered to teach her how to use it.