The title is not wrong in any way.
The two are by no means incompatible.
They could be considered opposites in the way “Shirt” and “Wool” are opposites. Just because something is made of wool does not mean it can not be a shirt at the same time.
So too with the terms “Prostitute” and “Slave.”
Prostitute means that sex is being performed for material benefit. Slave means a human’s body is controlled by another.
While one may fit only one of the two descriptors, it has sadly been common that both applied to the same individual. Kind of like there have been a lot of wool shirts over the centuries.
It says she was “ex-prostituted” not “ex-prostitute” That kinda implies she was prostituted out by someone else. This same article also talks of a “brothel” so I’m assuming it applies to this woman. Now days women who are in brothels are held against their will as sex slaves. This is not the image of “Gunsmoke” with Miss Kitty running the show. This is a place where women are caged like animals and used only for sex.