.. How do I get the ghost to talk to me?

This is going to be a multi-stage process. Did you try just talking to her?

She thinks she's still in her apartment and refuses to accept that anyone could be there talking to her because her door is still closed and nobody knocked.

Saying "knock knock" doesn't work; you need some actual knocking. Lauren could help here.

Click on the gate, choose "chat with Lauren" and "ask for help," then ask her to knock on the gate door. (You can also ask her to do a bunch of silly stuff if you want to make Joey giggle.)

This gives you limited access to the woman ghost. If you run through all the conversation options, all you'll learn is that she lived in Apartment 3D. That's important, but we clearly need more information.

How can I find out more about the ghost?

Once you've talked to Harriet Sherman, talk to Mavis again. This time tell her you're her son.

Run through all the conversation options to find out all kinds of good information --

-- including the name of her son, her ex-husband, and that New Yorker reporter who talked to her.

How do I find Mavis's son?

How do I find Joseph Mitchell?

How do I help the shut-in move on?