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.
There's precedent for us not seeing her do that explicitly but assuming it happened. Think about how whenever some crew had to leave the bridge in TNG a bunch of extras would rappel in from the ceiling, unasked, to fill their stations.