I have heard it used to describe both manager and the kitchen lady. Sometimes both are the same person.
When manager and kitchen lady are two different women, I believe that Emo usually means the kitchen lady.
My Korean friends tell the that the word actually means aunt.
Concur with Torito. The Korean translation for 'aunt' is 'imo' and for 'house mother' is 'jib-ui eomeoni' (Google Translate), and so the girls just abbreviate 'emo'