Totally agree to all of this.
Decomp, esp the attraction of blow flies, is extremely fast. I posted in another thread that this summer I had a baby bird in a nest that was a jumper who didn't have feathers to fly yet. I had checked on him and an hour later went out and he had jumped and got hung up in that hour and he was COVERED in fly's and it was one hour from the time he was last running through the yard with his mom freaking out and me putting him back in his nest. I quickly buried him to stop the flies but it's THAT FAST.
So with someone the size of your average 1 year old, if she died around 3am, and LE wasn't called until 8:12 how many different flies and other things had already come to aid in the decomp process? I know thats horrible to think, but she was wearing black, they looked through the culvert but people were looking for a 3 year old, people don't think of a 3 year old as "small" like an infant even when you are told height/weight. I mean, look at the pic of her with her sister, a year apart and a full head and a bit shorter! How easy would it have been to think this tiny little bundle wasn't just a piece of fabric, or a bag and completely overlooked as being Sherin because the size didn't fit what people expected. It's horrible to think about but necessary when it comes to accepting that she likely wasn't moved.
Of course, the ME should be able to give a decent idea of if she was moved or not, but for me its easier to accept that people saw her and didn't even realize it than to think that someone was able to pick up a body that was in full decomp, move it through a busy area with neighbours and LE all on high alert and crawl into a tiny tunnel with her and place her inside... Whoever did that would have likely vomited, would have clearly been very suspicious, and would have the "smell of death" on their clothing and body.... is it possible? yes... but it's also highly unlikely....
ALL just my opinion