So blocking is meaningless. Think about it. Even if there is no male model, there will be no shortage of handsome guys around beautiful women.
What should be yours is yours, not yours. There is no point in stopping it.
It is better to trust her, give her space and let him do what he wants.
Being a college model does not mean being a model after graduation. It's just a hobby, and it can also cultivate temperament. There's nothing wrong with it. As for the hidden rules you said, it depends on her nature.
Hidden rules don't force you with a gun. You want to be hidden. Everything is decided by your heart.