When we call an old lady whom we don't know well, we can call her "이모". For example, if you eat at a Korean restaurant and you need some more side dishes, you can call "이모" to a woman working at the restaurant to ask more side dishes. We don't use "고모" to call a woman we don't know well. We use "이모" mostly. So it is cprrect for Haru call 2NE1 members '이모'. As 2NE1 members are not married, Haru can call them "언니", as Haru is a girl. Calling a woman who we don't know '이모' sounds strange for foreigners, but we use the word to make a woman feel more comfortable and familiar. Thanks.