If you're still going to let her do your touch ups, then I don't see where you're letting her down at all.
Just cancel your appointment for Saturday, (saying that you don't need her to do your hair - if asked... which is the truth) and reschedule later for the next touch up.
If she asks why only touch ups, tell her because now that your hair has grown out, you can handle it a little better on your own (which would be the truth too right?) If she gets offened, oh well... A good stylist should love to see her clients properly caring for their hair with or without their help.
My stylist goes to my church and I only go to her for touch ups. Even when I do styles or expirement on my own, she's always talking about how shiny my hair looked or how she loved my styling. She's confident, secure and doesn't make me feel like I have broken up with her when I cancel to save money or something. She even sells products that she uses on your hair, tells you how she used them so you can do it at home.