In this case, the handkerchief is the evidence. As comparison to the naive wife, Iago is the clever thinker who he knows Othello is absolutely faithful to her wife, and by backbiting Desdemona's so-called "dishonesty"," he could ruin Othello's happiness in this way. Othello once expresses his love towards Desdemona that, "My life upon her faith!--Honest Iago, My Desdemona must I leave to thee "( I.iii 295), and this quote clearly states that Othello takes Desdemona's faith as his life, without Desdemona's faith his life wouldn't be completed. .
And now turns into the main part of unfolding Emilia's character in the play. The remaining question would be, how much of, if there is any, moral responsibility is to be attributed to Emilia for her to involve in Iago's plot. Many may think that, Emilia is compelled to lie due to her dominant ideology of wifely virtue or the conception of women's social norm; she might anyway killed by Iago in either ways of whether she steals the handkerchief or not. Emilia, imagines that stealing the handkerchief will not only promotes her husband's love towards for but also gives a hand to her husband's intention. However, I do not think that this is the correct understanding; to both getting freedom and gaining equality of love from Iago as Othello and Desdemona's ideal marriage, are the major reasons that initiate Emilia's lies. She chooses to lie to Desdemona in the first place was that to deny a hideous truth that she finds difficult to acknowledge: Emilia envies of Desdemona's happiness and hopefully would succeed to gain love from Iago by fulfilling what he wants. .
Emilia knows that Iago is anxious in obtaining evidence to prove Desdemona is guilty, and when Emilia picks up the handkerchief which Desdemona has accidentally dropped, Emilia is not yet confirmed with the reason of his wanting. Emilia immediately leans more on the side of achieving her own desire to please Iago against Othello rather than her knowledge of the import the handkerchief holds for Desdemona.