To add to the previous editor's comments, Emilia's loyalties shift from her husband Iago to her mistress Desdemona.
We see Emilia stealing the handkerchief for Iago in Act 3. It's an harmless act, she thinks, and she has no idea what her husband intends to do with it. She also has no idea that her husband is a villain. She is too quick to think his failings are the general failings of all men, not just her husband: "Methinks it is the husband's fault if wives do fall," she tells Desdemona. So, when Desdemona frantically searches for her handkerchief, Emilia stands by silently.
However in Act 5, when Emilia discovers her dying mistress, she threatens to expose her murderer to the world. "I care not for thy sword," she tells Othello who has threatened her when she is about to make his act public. This is a powerful act of courage. She defies Othello--her superior, a man, an armed man. When Iago tells Emilia to be quiet, Emilia tells those around that "Tis proper I obey him, but not now." She tells the truth about the handkerchief and says to Iago, "Perchance I'll never go home again."
The one person Iago misjudged was his wife. He assumed that she would be his loyal, faithful, and submissive wife. In the end, Emilia valued her friendship with Desdemona and the truth more than her vows to her husband.
" . .. speaking as I think, I die, I die," Emilia's last words are to placed by her mistress's side. She has given her life to exonerate Desdemona.
Emilia is a key character with regards to the theme "loyalty vs. betrayal." In Othello, Iago tells Emilia that she must steal Desdemona's handkerchief. Emilia knows how dear the handkerchief is to Desdemona having heard Desdemona speak of the circumstances under which Othello gave her the handkerchief as a gift. However, Emilia is loyal to her husband Iago and wants to please him, so she betrays Desdemona's confidence to steal the handkerchief. At the end of the play when Iago's scheming is revealed, Emilia then betrays Iago and admits that she was the one who took the handkerchief that ended up in Cassio's hands. She then resumes her sense of loyalty to Desdemona by showing regret and remorse for what she has done. Therefore, Emila exhibits acts of both loyalty and betrayal during the course of the play.