Many people sympathise with Emilia because Iago treats her badly, and uses her as a "tool" for sex and his plans. But how much should we really sympathise with her? And what other reasons are there to sumpathise with her?
She's a very sympathetic character since we realize, even if she doesn't how evil a man she is married to. It isn't easy being married to Iago, and she is obviously aware of that fact, but by act 4 she still has absolutely no idea how truly corrupt and perverted he is. The Fishburne film, by the way, does a splendid job of presenting their relationship, and the woman who portrays Emilia in that film is superb. Scenes are available on YouTube.
Emilia is used as a pawn by Iago. We do feel sorry for her because of the way she is treated. On the other hand, she allows herself to be used. We loose some of the pity for her because of her own actions. Of course, she didn't necessarily understand the consequences of all those actions. Is she as naive as she seems? Is she scheming just like Iago but for her own goals? How does Iago's treatment affect her? Personally, I didn't feel much sympathy for Emilia. I usually found her to be a bit conniving in her own right.
I don't think that she necessarily allows herself to be used- she is just so devoted to her husband that she is able to see past his 'faults'. What possible motives could she have to scheme against anybody? Perhaps she is jealous of Desdemona's marriage with Othello, and when in act 4 scene 3 she offers her opinion about adultery, maybe she is really trying to corrupt Desdemona. How come you don't sympathise with her? Surely this is unfair having seen her relationship with her husband..