P.M.
I think that you're tipping just fine. i usually tip about that amount too. My sister works in a hair salon and she says 15% is good. Some people don't tip at all and that's after a hair color or perm. She's even cut several people at once from the same family adn only gotten a dollar. But ata place like Supercuts where it's only about 15 for a haircut I usually give 2 or 3 dollars.
I think if you weren't tipping good the stylist you use would become "unavailable" when you called for an appoinment. You can always give her something extra during the holidays if it's someone that you use all the time.