After completing Stealing Independence and Sydney moving to the Museum of History, Sydney may just stand around in the Museum of History without actually heading into Underworld itself. Normally this wouldn't be so bothersome if she'd set up shop there, but she doesn't until she actually goes into Underworld.
I've been racking my brain for days wondering why this was happening in my game till I decided to do a moveto.player command on her while I was in Underworld. Lo and behold, she greets me with post-Stealing Independence dialog and is now a vendor!
Can't wait till 3.0, I remember reading one of the changes being that she'll sell a lot more ammo since she did mention that she was an ammo vendor. Will be great to have DC's own Quartermaster Bardon, I've got more caps than I know what to do with and I haven't been to Vegas yet to splurge on the GRA unique weapons.
Greta also just stood in front of the Underworld entrance, probably from her smoko she normally takes at night.