Hey, really have your friend check into this because:
I broke mine when I was 18, doing a backflip off a high dive but landing bottom first. I sank to the bottom and my boyfriend had to pull me out. The pain was excrutiating.
I did as the doc said - sat on a donut pillow, yada yada.
Now, years later with all these back problems, I have had 2 manipulation therapists SWEAR that my tailbone is in the wrong place big time, and they both believe that if it had been correctly repositioned, I might not have had these back issues.
With it being in the wrong position, it pulls on the wrong muscles or does something strange.
Anyway, if I could go back, I would get extra opinions and make sure it doesn't need to be "put back". That wouldn't be a fun experience, but neither is years of back trouble because it wasn't, either.