Been following along silently but here's my opinion.
The key to this case lies with what exactly she said to the "friends" when she left her dog. IMO, it's more likely she said "hey I need to...blah blah blah.....watch my dog." Be it go to the bathroom, go back to the apt to grab my phone, go talk to so and so over there, something. Saying "hey watch my dog" and the other kids not asking and her not saying more seems unlikely.
IMO, her intention was totally benign and she met up with someone on the way to wherever she was going. For example, could be a person in the parking lot, coming out of another apt, just hanging around. They either snatched her quickly or had a ruse where she willingly went along. I'm sure all the vacant apts and those being renovated have been checked. I believe that's a probable crime scene.
She was likely placed in the dumpster after dark. I haven't seen any mention of a large scale search of the apt complex the first night. Police and parents believed she may have been at a friend's house. Had residents been alerted there was a missing child the night of the 19th? If no one knew, no one would pay much attention to someone throwing a bag, suitcase, whatever into the dumpster after dark. She would have fit in an old suitcase or plastic bin that broke open easily while being transferred from the dumpster to the truck then truck to landfill. That's why her body could be secretly placed in the dumpster but out in the open at the landfill.
All of that is my opinion only.