To describe Desdemona as guilty is to mischaracterize her. After all, one of the central elements of the tragedy is that Desdemona herself is innocent of the accusations leveled against her. She is a victim both of Iago's manipulations and of her jealous husband's abuse, and this leads to her being murdered by Othello at the end of the play.
The key factor to keep in mind is that Iago is a liar. He is continually manipulating the action of the play in order to rouse the jealous mistrust of Othello, convincing him that Desdemona is carrying on an adulterous affair with Cassio. But the reality is otherwise: Desdemona is and always has been faithful to Othello himself, even in the face of his jealousy and abuse. In act 4, scene 2, when she calls herself Othello's "true and loyal wife," she speaks truly. Even if Othello is convinced she is an adulteress, in reality, she is very much the opposite.
That being said, however, she is not entirely without deception. As we learn in the play's beginning, she married Othello in secrecy and against the wishes of her father. It is an interesting thematic wrinkle within her role and characterization in the play, and from a purely patriarchal culture (as was common in Shakespeare's time), such a decision might well have drawn censure. Yet when seen through modern sensibilities, it would be patently unfair to condemn her on these grounds and label her as morally culpable in some way for not subordinating herself to her father's wishes. However, even if we should not condemn her, we should be aware of how this earlier act of deception is weaponized by Iago himself for the purpose of turning Othello against his wife.