Just some thoughts:
1. Alcohol: The article from the Ottawa Citizen linked up-thread states (on the second page) that a road-side screening device test was administered to the driver, and “registered zero alcohol content in her blood system.” Given that screening test, the officers had no grounds to ask for a more thorough breathalyzer test at the police station. The road-side devices aren’t as precise as the breathalyzer test, but a reading of zero is pretty significant.
2. Cell phone: was there any evidence, available to the police at the time of the accident, that the driver had been using her phone at the time of the accident? Canada, just like the US, has constitutional prohibitions on unreasonable searches and seizures. If the police did not have any evidence that she had been using the phone at the time of the accident (and I’ve not seen any mention of that in the news articles, just speculation; please correct me if I’m wrong), they did not have grounds to seize her phone on the scene, nor would they have been able to get a search warrant to seize it.
3. Leaving the Scene: how many times have we seen it posted, right here on the SDMB, that if detained by the police, it’s always open to ask, “Am I under arrest, or am I free to go?” The police have the power to detain to take witness statements, and usually the first witness they would want to interview is the driver of the car. If they had taken her statement, and they did not have grounds to arrest, I don’t see any basis to hold her if she asked that question. It may have taken longer to take the statements from other witnesses, simply because of the priorities of securing the scene, tending to the injured, and taking a statement from the driver (if she gave one; I haven’t seen anything one way or another). But, with a zero read on the road-side screening device, if she asked that question, the police may have been required to let her go: like the US, Canada has constitutional protections against arbitrary detention.
4. Police Don’t Rule on Negligence Issues: it’s not relevant to a civil suit that the police declined to lay a criminal charge. Criminal charges are based on intention or recklessness, not simple negligence, and have to be proved beyond a reasonable doubt, not balance of proof, which is the test in a civil suit.
5. Court costs: standard in civil matters in court cases in Canada, and usually includes some portion of lawyers’s fees.
Usual disclaimer that none of this is intended as legal advice, simply to comment generally on a tragic matter that is raising public discussion. My heart goes out to the parents of the kids.