The point wasn't that she was underpricing herself: it was that by charging more she gradually found herself offering quite different services.

For $300/hour her clients were still wishing to physically get the most out of her (and, apparently, themselves) during the one hour; for $500/hour she started to find clients who were more interested in high-class flirtation, having a wife replacement for the evening, and the sex portion was reduced to a lot less.