Is a virgin's silence counted as consent to be married?

Yes, a virgin's silence counts as permission, while a previously married woman must state her consent clearly.
The Prophet ﷺ said that a previously married woman is not married until her opinion is sought, and a virgin is not married until her permission is sought; when asked how a virgin gives permission, he answered: "She is silent." This is because of modesty. But if the virgin weeps in disagreement or states an objection, her silence can no longer be taken as permission. In Malaysian practice, the bride usually signs a consent form before the registrar. See Marriage wali.