D.B.
Not if it's the same stylist - it's her mistake. I'm not sure you should have been so generous in the first place if she didn't do the work you discussed. But maybe you couldn't tell until you got out and into the natural light?
If it's someone different fixing the mistake, then the service should be free but I would tip her - it's her time, and not her fault. This is where the savings from the first tip might have been useful.