I did it!
The disappointed client from the other day was very pleased with the massage she received from me.
Not only did I redeem the spa's reputation, I also landed a loyal client who already booked another appointment with me two weeks from now.
But the most important thing about all this is in her reaction as she exited the room: not to go into too much detail here, but she has a chronic condition, and she told me tearfully that for the first time since she can remember, she was able to turn her head without pain.
That's better than earning brownie points with the boss any day.