The bottom line is she provides a service to you. Like an employee. You don't owe her anything.
I think you are certainly within your rights to try someone new, something new, etc. without having to explain yourself to her.
Besides, it sounds like there have been extenuating circumstances, so I'm sure she'd understand you getting your haircut elsewhere.
I'm of the opinion that since I'm not a higher maintenance sort of person, I get my haircut when I need it, not always on a schedule, don't do my nails, and occasionally do (scoff) bottle color. My stylist knows this about me, and doesn't seem to mind. He just gives me fabulous tips when I do schedule time with him - after I get tired of cheaper cuts and bottle color.