AS keep gosssiping to Egwene about Halima doing this and that. It's also mentionned how often she's with Delana, and how inappropritate their relationship seems to be (Halima is too disrespectful). By all evidence, Halima spent most of her time in the camp, except for a few exceptional errands, like Forsaken meetings, and short "personal time" for her little schemes elsewhere.

It's not as easy as you make it sound to slip away. People expect Halima to be around Delana as her secretary. If she kept coming and going all the time, this would have raised attention. AS feared spies in the camp, and that sort of thing would have raised attention. Most likely, Halima vanished from inside Delana's quarters, for relatively short periods of time where it wouldn't be noticed she was unaccounted for. The longest she may have been gone from the rebel camp was during the Cleansing, most likely.