Right to all these people that are having trouble with Jan not turning up (if you've destroyed all the AT-ST's). She's turning up in a place you haven't been yet. Remember the hanger you went in to switch the shields off? Well if you go along the top catwalk around to the other side, you'll be greeted with some stormtroopers and you'll know where to go from there.
Hope that helps - Koounaaar