Some documentation on drowning and asphyxia for those interested.
http://www.forensicpathologyonline.com/E-Book/asphyxia/drowning
Stryker57's posts:
http://www.websleuths.com/forums/search.php?searchid=5417564
Lavaland's posts:
http://www.websleuths.com/forums/search.php?searchid=5417568
I spent many years counselling suicidal people and been there myself. Usually the methods that come to mind are the fastest or most convenient - unless you want someone to suffer afterwards. When considering other people, ie "I don't want them to find me", usually a more remote place is discovered, if ever at all. She had to know she would be found in that culvert, and that her family would learn the details, otherwise if she didn't care, there is no explanation for why she wasn't in the car or her home. As someone else pointed out, it is really difficult to kill yourself in the manner she was found without the help of drugs, alcohol, or other devices to restrict your survival response. We do her an injustice by calling the bag found with her an Exit Bag - it was a plastic take out bag. The two things are very different and IMO one implies premeditation and the other doesn't. It is entirely possible the bag was already in the culvert, came to be around her head from moving water or some other means, and has nothing to do with her death. LE may have forensic evidence to the contrary - we don't know, but I do agree with some of you that this is either a diabolical homicide, or a perplexing suicide with one or more red herrings.
Her keys, phone and wallet are probably in a landfill, which wouldn't help clarify anything if they were found at this point IMO. If you look at all the facts we have and the timeline, none of it adds up to support either finding, so I can completely understand LE's statements.