Glitterbag is using one of the oldest sexist tropes that women are objects of sexual desire.
She is assuming that your wife can find a lover simply because as a women she is sexually attractive (in a way that presumably a man isn't.) Of course this isn't true. It is easy to find women complaining that men don't find them attractive.
There is an old saying ... People don't pay a prostitute for sex, they pay them to go away afterwards. Prostitution is honest, you pay, you get what you want. There is no need to play games, or worrry about emotional consequences.
I don't recommend it. But I don't condemn it either.
I do think it is cheating... which was the question in the first place.