.. How do I defeat the vengeful ghost in my apartment?

After you finally break into Charles's email --

How do I learn Charles's password?

-- the Countess will appear, with violence on her mind. Time to run away! For a bit, at least.

When Joey grapples with the Countess, leave the apartment. Now where?

The elevator is stuck on another floor, and most of the other doors are locked. Is there one that's open?

Go into the trash room (the dark brown door) and wait. When Joey and the Countess go into Nishanti's apartment, the elevator is still stuck, so the only place to go is back into Rosa's apartment.

As Rosa now says, she's pretty much stuck. If she leaves the building, Joey will perforce be dragged along with her, and Joey is the only thing holding the Countess back. Rosa needs help from another source.

As Rosa flubbers around in her apartment, she says that her aunt defeated the Countess 30 years ago. When she says that, Auntie Lauren's picture starts to fall off the wall. Is it a sign? Heck, it's something. Take the picture.

When the Countess returns, use the picture on her.

Two Joes in a Diner