We can't tell without more context. Can you give us the name of the story?
I'm just guessing here. I think a convent might give temporary shelter, unconditionally, to girls in a dangerous situation.
However, to join the convent and become permanent members, they would need to become members of the convent's religious order. They would need to become nuns. They would need to accept the convent's religion. But that would not be enough, they would also have to accept a large number of additional, strict rules of the order itself.