I would say no, she could not use area attack as she is defending against the creatures' attacks.
Although the way it plays is the same, in the Tomb phase you are rolling for defense rather than attack.
And yes, as you said, you can't "Area Attack" when the creatures are attacking. Because, it's not your turn and you're not spending an action do attack. Additionally, you wouldn't need to area attack because they will all attack you anyway (if you're alone in the room and / or have the most shards.