Eventually you will return to UNATCO HQ, but everybody will be hostile toward you. You need to kill all enemy combatants on this level. This doesn't include the secretaries, but it does include all the troopers, Anna Navarre and Joseph Manderley.
If you've killed Anna in the 747 before, she obviously won't show up on this chapter, but this doesn't void the achievement. The way you kill her also doesn't matter, so you can get the achievements related to her killphrase in one run: