In Act I of Othello, Desdemona and Othello are very clever. If they would have asked for Brabantio's permission privately to be married, he would have denied them. Worse, he might have secretly used his power as senator to separate the couple. Desdemona knows that Brabantio would not condone the marriage for the following reasons:
- Desdemona is white; Othello is a "black-a-Moor"
- Desdemona is young; Othello is old (close to her father's age)
- Desdemona is a senator's daughter; Othello is an immigrant
- Desdemona is a Christian; Othello was once a pagan
- Desdemona is a civilian; Othello is a military man
As a result, Desdemona and Othello elope first and ask for permission publicly later during the Duke's senate meeting. In this way, they are awarded three-fold:
- Othello is named General and ordered to Cyprus
- The Duke grants permission for the marriage (and Brabantio must also agree)
- The Duke allows Desdemona to accompany Othello to Cyprus (a kind of honeymoon).
So, to your question, I wouldn't say that Desdemona is necessarily deceitful. Certainly, Brabantio thinks his daughter is deceitful when he tells Othello:
But, then again, Brabantio is a racist, sexist, and an elitist. So, I wouldn't buy into his belief that all women are evil.
Rather, she adopts the clever strategy of "act now and ask for permission later." Also, she and Othello powerfully use rhetoric publicly to win their argument against Brabantio.
That being said, the Desdemona of Act I, a clever vixen who uses public rhetoric to get her way, abandons her identity and this strategy after she is married and moves to Cyprus. There, she is a mute victim who refuses to even cry for help as she is being murdered in bed by Othello. She's a strange character. Shakespeare shows how marriage makes strong women completely powerless.