I keep listening to the video of the press conference, looking at the map and reading the news reports. She and CR leave the bar, go to her apt, the 2 remain in the lobby where CR has an "encounter" with friends of LS's boyfriend. She walks him home. Video shows them leaving her apts. together around 2:40 am. Around 3am a video captures her and a male companion (CR you can deduce), walking in the alley between 10th and 11th (going to his apt). This is the last detail the PD says they can confirm absolutely she was seen (last hard evidence), and also where a set of keys were found (yet to be confirmed as hers). Based on eyewitnesses though, someone saw her leave CRs apt buildings, and last seen as she turned on 11th to head S. on College.
So, she wasn't in the alley then, on her return trip. I think indeed someone was waiting for her to be making her return trip back to her apt.