She may have rage quit in a dungeon/instance in Lower La Noscea (can't think of what it could be - a job quest perhaps). If you quit during an instance it shows you as still being online until you next login. I got worried about a friend that was showing as being in Snowcloak for over 3 weeks. I'd contacted him via Twitter after a day or so and found out he'd rage quit. It was only maintenance that kicked him out!