You know that's odd. When I served in the military you didn't abandon your post without proper authorization prior to leaving it. In fact it was a general order that you did not leave your post w/o permission.
If she was temporarily in charge, she could have left the post, but that would require she appoint someone, no matter how temporary, to assume command.
It's not odd; it's not abandoning her post: she walked to the elevator and asked the captain where he was going, which as I indicated and you quoted, is information she would be asked and needed to know.
Then she accompanied the captain, who could have reprimanded her had he thought she was abandoning her post in that situation. As already pointed out, she's not alone at communications.