Could we try to speculate on possible scenarios, and organize our ideas into categories? This is what I can think up so far. I know we can brainstrom more possible scenarios.
One scenario - Look at the husband. Like many have said, it is usually the husband, sad to say. He killed her by accident (an argument got out of hand), then he thought up a "cover story" and hastily made it look like she had been abducted on the way to work. Would explain elements that appear to be "staged", might explain timeline problems.
-or-
He killed her on purpose, and premeditated the "crime scene". Tossed her body in the North Saskatchewan River? Motive? Did not want another baby, trapped in marriage, girlfriend on the side...
Second Scenario - Staged her own disappearance - reasons? Trapped in marriage? Has boyfriend? Running off with said boyfriend? Baby is not hubby's, and the truth will come out eventually, so cannot stay in marriage? Does not want another baby, wants to abort? Prenatal tests indicate child has birth defects, does not want to carry to term, hubby would never agree to abort? She is suicidal and staged "crime scene" to spare family from knowing she chose suicide, walked to North Saskatchewan River and jumped?
Third Scenario - Crime Committed by Third Person - someone she knew - such as a boyfriend, maybe the father of the unborn child, who does not want her to have his child, or who is maybe married to someone else? Or someone she knew, such as a friend or relative, who was angry, jealous, whatever.
Or by someone she did not know - a perfect stranger, who somehow managed to get her to pull over through some sort of trick, in order to harm her. Or, for some reason, she pulled over on her own - I used to pull over to vomit from morning sickness, and with my 2nd and 3rd child, my morning sickness went into my 5th month. If she pulled over on her own, she may have just been in the wrong place at the wrong time, and been jumped. Or perhaps she witnessed something she shouldn't have witnessed, some sort of criminal activity in the park where her vehicle was stopped.
This is as organized as my thoughts can get, as I puzzle over this case. I would love it if some of you sleuthers can think up additional possibilities.
**I hope I don't appear to be disrespectful to the Whites with some of my speculation. I am very sensitive to casting victims in a negative light. This is not my intent....