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The actual feminists say, "consensual, mutually beneficial, what's the problem? She sounds like a boring and graceless person which reflects poorly on her beau, it's hard to imagine her conversation has lasting depth or sparkle, and her rates are certainly very low. But deciding to be that way is her choice."
I think it's great that two so emotionally damaged people have managed to forge a workable relationship. People who can't relate flexibly end up with some compromise like bondage, marriage, payment, whatever. It's great that these two are unabashed enough to find their happiness.
Relationships are fraught with fear of rejection, commitment, inadequacy, blah blah blah, and strategies like this one help dampen those pangs for they who are too sensitive.
She's not a prostitute; prostitutes are indiscriminate. She's not a gold-digger, those angle for marriage. She's a kept woman. Time will tell whether she jumps one way or another or blossoms into something unexpected.