Which one is used more often in restaurant to call the elder woman?아줌마 or 이모?

I found I couldn't post the question successfully. So I post it here.
In some TV series, I found when you order food or ask for help, there are two salutation to call the elder woman:아줌마 or 이모. Actually, we are taught to use 아줌마 in the textbook. 이모(姨母) sounds like the sister of our mother.
Who could kindly let me know? Thank u~