The crash had two problems- Karen's airbag did not deploy, which it would have done on a frontal impact, and due to the nature of the frontal impact, the passenger could not have been thrown out of the side of the vehicle as shown. In a frontal impact, passengers are thrown forward, not to the side.
The AC compressor that Denis is repairing is clearly a prop. Units such as the one shown are not installed halfway up a wall, they are installed at ground level for accessibility and due to their weight. The unit shown only had one line running to it. A compressor requires two lines plus heavy electrical wiring.
When Karen, who lives in Kansas, does a web search for her symptoms, the term "colourless" is returned, which is the Canadian spelling. She was clearly using a web provider based in Canada, where the movie was filmed. The detective also as a noticeable Canadian accent.
The gun can be heard being cocked after Karen picks it up after the crash, but it was already cocked when she picked it up.
Karen gets two hangup calls in a row and says she does not know who is calling. She later tells Donna they are from a private number, so she has caller ID. A woman in her position with a history of bad relationships would utilize caller ID's ability to block unwanted calls to avoid that type of call.