Just speculation here - and I'm admittedly never the best at piecing together timing, cameras, etc., so forgive me if I'm missing a piece. But, could LS have arranged to meet her dealer at Smallwood? Maybe that what the intended place (her apt, perhaps?) for the re-up to take place, or for her to at least sync up w/ dealer & co. to go elsewhere.
I can imagine a few things happening if that were the case. Maybe LS then realizes it can't happen in her room since she can't get in. Might annoy the dealer a bit since he came all the way out there... But Lauren wants her high, so she follows to a new location. Maybe even "borrowed" JR's apt for this purpose?
Secondly, and independent of my first thought... I wouldn't be surprised if Lauren borrowed a phone, called her dealer, and the convo went something along the lines of "hey, it's ME, Lauren... Meet ME at my apt...etc." Deals aren't usually a meet "us" type of scenario, unless these introductions have already been made. Might explain a lot about why someone was NOT happy to see her walk up with CR. And, the likely (IMO) "Who's he? He's not coming with us" reaction (which I'd assume would be conveyed which much less pleasantries) would, IMO be a sure catalyst for words to be exchanged - words that could easily escalate to a physical altercation.
JMO...