It seems to me like this will be solved by the phone data. Please correct me if I'm wrong but I think a poster in a previous thread said that the GPS data will be available without the actual phone. If that is true, we will likely be able to see if she walked to the culvert or if the phone traveled around.
I suspect the police have additional evidence but they didn't really want to release anything until everything was completed. They felt pressure and have released some evidence to show the public is not in danger but have held back other evidence that might be sensitive for the family.
However, they have not said anything about the toxicology results, which are most likely negative for everything and the autopsy is complete. If the time of death is not Monday, that could be a problem.
The police are doing a poor job revealing information about this case. If they have substantial evidence of suicide, it needs to be presented to the family to give them the chance to address it if they choose. They need to stop revealing bits of information to individual reporters and have a press conference.
What are the toxicology results? What is the time of death? Did the police check homes and businesses for video surveillance along the possible route? Were there any videos of her walking?