Sibille works in one scene at the diner and it's dark outside. But it couldn't be dark because a few scenes earlier she said she works until 6pm, and in summer it's still light then.
When Nathalie tells Gabriel that Sibille is dead, Gabriel says that Sibille was squashed, but he couldn't know that because Nathalie didn't tell him.
Sibille's mother locked her in a room with a glass door. Sybille was desperate to start a new life and had everything organised (train ticked, accommodation, training placement). It would seem logical that she smashed the glass and fled into her new life, rather than killed herself.