This is what I think. At the apartment complex that she shot herself in, the woman who said that she had exchanged apartments with her is the person she had a relationship with. All of the rest, except for the fact that she did come from Ontario and met the two old people on the plane, and she was looking for acting work, all the rest was in her mind.
She came to LA looking for work and met that other woman in the apartment complex, who came to her door to get her box of stuff near the end. She had a relationship with her and then they broke up. From that point, she descended into a dillusional psychosis, not leaving her apartment for weeks. The blue key was real, it was the key to her apartment that her ex. gave back to her.
Everything else was a backwash of symbolic psychosis for her coming to the point of shooting herself.
In the restaurant where she hired the hitman is the main turning point for her, the point that she decided within this psychosis that she wanted out and went past the point of return. The blue box is her mind. The blue key, the finallity of her girlfrind returning it, totally ending the relationship, was the thing that started her in the descent.
The old people in the end was the thing she remembered as the point where she stepped off the plane in LA to lose her innocence, and they were her last innocent encounter, so, in her mind in the end, they got demonized, in fact her innocence, her only true thing before that she had to hold onto, became completely corrupted, as in destroyed, the only way that she previously knew how to live sanely. Hence, the overall theft of this posession of innocence took her sanity.
