How does Emilia function as a foil to Desdemona?

After finding Desdemona's handkerchief in Cassio's lodging, Emilia plans to have a copy made of it so she can return the original to Desdemona but give a copy of it to her husband Iago who has been continually asking her for it. Emilia has no idea Iago wants it to convince Othello that Desdemona is being unfaithful to him, and before she has a chance to have a duplicate made, she gives it to him in an attempt to get some attention/love from her neglefctful and emotionally abusive husband, Iago. Iago proceeds with his plan and is successful in convincing Othello his wife is cheating on him with Cassio, putting the tragic events of the story into motion. Thus, Emilia unwittingly is a foil to Desdemona.