Emilia is the first to suspect the reason behind othellos behavior. Consider: why would it be her out of all the characters? Emilia reveals the source of iagos suspicions about her othello having an affair- what made iago think this?

I think that deep down Emilia knows her husband is a nasty human being. She is intelligent and, unlike her husband, is loyal to the people she loves. Emilia is smart enough to put the scarf incident together with Iago's treachery. I'm not sure about your last question.