A news article about this case said that DW had last been seen at a
business in the 300 block of Owen Manor (as opposed to last being seen in the parking lot or by her ex, when the child was dropped off). The only building there houses 2 businesses, Wilson landscape/garden supply/home goods/cafe (closed at 8 pm), and the Stoked Centre, an indoor family entertainment center. It appears to close at 10 pm, with bowling until 12 am. I think it's possible that after the father dropped off the son to DW (exact location unknown?) at 6 pm, she may have taken the boy to the center. If LE already knew when she left that business, they knew she could not be at the river at the same time. I can think of several motives to take the boy there (get him exhausted, an activity until it was dark). Or did DW get something to eat and/or something they needed for the trip? Maybe the river staging was done at dusk (sunset 9:14 pm), or even later, as she couldn't risk a search (phone ping, contacting the father) starting on the same evening she was disappearing if her blanket and purse were found in the daylight. I think she would have wanted a few hours of a head start, in case the husband convinced them that she possibly fled with the child and they started watching the highways.
If DW managed to leave a vehicle, near where her truck was found, earlier in the day, she could have even done the staging all by herself. I think that LE already knows the other vehicle involved and most likely the accomplice.
Since there has been recent news coverage of river rescues and drownings in that area, perhaps DW got the (naive) idea that it would immediately be thought DW and her son had drowned and further investigation was not necessary. After a futile search for their bodies, it would be presumed they were dead. It's not uncommon for bodies not to be found for a long time, and sometimes drowning victims are never recovered. Maybe she thought, again naively, that she'd just change her appearance, lay low for a while, then start a new life since no one would be actively looking for them. She may have thought she could eventually contact her family.
On July 3, 2022, a missing 7-year-old's belongings were found on the riverbank and it was correctly assumed that he had gone into the river. This was right in town, I would think DW had heard about this.
https://saskatoon.ctvnews.ca/7-year-old boy-dead-in-saskatoon-following-river-incident-
"A seven-year-old boy is dead after an incident on the river over the weekend. On Saturday around 8:30 p.m., police were called to the east bank of the South Saskatchewan River near Victoria Avenue after a boy was reported missing. Officers searched the riverbank and surrounding area and found the boy's discarded belongings, according to a statement from Saskatoon Police Service (SPS)".