Guests that would be most interesting: Prisma's ex from the building or the police detective assigned to her case. Other possibilities: the E-bar bartender, the person who saw her crying on the garage roof, the tree friends that she spoke with before she disappeared, especially her last call, the babysitter, or any other Prisma's friends that haven't spoken out. Unfortunately most people from the list would likely refuse to participate and some might not be contactable. There might be others (e.g. the Jeep owner) that would probably be reluctant to speak publicly.
I'm not sure why the information on the time of her last ping is being kept secret by police, so I'd ask about that. IIRC her family called her that night. It would be good to know if her phone was still ringing or the calls went directly to voicemail. I'd ask the second to last caller if she was actually in the building's hallways when she asked about her ex's apt number or was she still on the roof? I'd ask friends if she had any history of drug abuse. How did she get into the state of confusion in her last call to the point of not knowing where she was at? Would alcohol intoxication alone have caused it? Did she simply get lost within the building and couldn't remember the building's name/address? How did the last call end? Was she in an enclosed space, perhaps in the dark? There was very little time between calls so I don't believe something significant happened to her by then (e.g. falling or being kidnapped).
So little information is out there regarding content of the last call and where she was at...I assume police know this information though and it's not helpful to them.