First, look around her apartment to see what you find.
There's a photo on the bookshelf that shows her and someone named Rachel who worked together.
There's also a letter on the table from an entity named STP. It's vaguely threatening, but not too comprehensible until we can find out what kind of company STP is.
In the lobby, look at the mailboxes to find Mailbox 2, which is Tiffany's. Have Joey stick his head into it --
-- to see a card he can't read, because it's dark. Does Rosa have a way to light it up?
Yes, she does. Examine Rosa's business card to find that it glows in the dark.
Put a business card into Mailbox 2, then have Joey look inside to see that the letter comes from R. Ubu. You may think you know who that is, but we need to help Rosa figure it out.
In the "Compare Notes" section of her phone, combine "Rachel" and "R. Ubu" to get Rachel Ubu. Oogle "Rachel Ubu" to get a coffee shop called Cup of Clay. Go there.
Rachel tells you that Tiffany was obsessed with someone named Ken, and they both worked for a temp agency. Could that be what the STP letter was talking about?
Combine "STP" with "temp agency" to get Sterling Temp Placement. Oogle it, then let's go there.
What can I learn at STP?
When you know Ken's place of business, go see him. He's not going to give up the info easily, but we know how to deal with that, don't we?
How do I get Ken to be honest?
That's all you can learn until Tiffany realizes she's dead.
How do I save Tiffany?