Gwen's group was in on her therapy.Think about it - they were there when she got there, they were still there when she left. They were there to help her face herself. Daniel and Andrea's issues were part of the act - Daniel leaving and coming back to show how common it is to relapse, and Andrea's death was faked to drive that point home (It's only Daniel who checks Andrea over!). Eddie Boone is only there to show Gwen that her relationship with Jasper is trouble, and after she gets out she runs into Gearhardt, who's just checking on how she's handling things post-rehab.
The limo driver got fired.Leaving the limo unattended with the keys in it. It was obviously some time until the bride and groom were supposed to leave - the cake hadn't even been cut yet.
This movie is in the same universe as 28 Days Later.The stories don't cross, but the rage virus is released the same day this movie ends.