The "waiting lounges" are the themed departure holdrooms.

The easiest-to-find place for her to wait would be the B2 food court (there's a 24hr McDonalds). The north and south sides of the terminal have 5th floor waiting areas with convenience stores (7-11 in the north and Familymart in the south); they're a little bit more convoluted to navigate to (you go to the 3rd floor, then go to either the north or south end, and then take a separate elevator up to the 5th floor), but they might feel better than a basement.