Omg, I just thought of something.
What if BB left for the airport and left MD home alone while DV was at work and then BB told DV he had to come home.
According to your time above. DV left work after an hour, so that means he was home after 10am. Who was watching MD in between BB left and DV came home. Hmmmm
or maybe BB was frustrated with MD cause she had to leave for the airport and DV wasn't home yet and she took it out on MD. Moo
Super interesting line of theorizing, IMO.
Pure speculation:
* BB is home getting ready for her trip. DV leaves to take the boys and Maleah to daycare. But he doesn't drop off Maleah after all (not sure of reason ... maybe M threw a fit, maybe she seemed sick, maybe some more nefarious reason). He brings her back home, not very happy about it which is why he is walking ahead of her on the camera footage. Maybe it just threw a wrench in his plans for the day.
* BB is equally displeased to see Maleah at home. The two fight about whose fault it is and who is responsible for supervising Maleah. DV is supposed to go to work, BB is supposed to leave for the airport. BB blames DV for not dropping off Maleah.
* DV insists he has to leave, telling BB she needs to either cancel her trip or find some other care for Maleah that day. He departs for work.
Then one of two scenarios happens:
1. BB is home with Maleah for that short time between just before 9 and 9:30. She is unwilling to cancel her trip and is angry at Maleah for being such an inconvenience. (Maybe she even tries to get some other family members to watch Maleah? But no one will). In her anger, something horrible happens to Maleah. She calls or texts DV and demands that he come home to deal. She leaves for the airport.
2. BB does not care that Maleah is home; she is leaving no matter what. She calls DV's bluff and tells him he'd better come home from work because she is leaving for the airport and Maleah is still home. He leaves work and is enraged by the situation and by the inconvenience of Maleah's presence. In his anger, something horrible happens to Maleah.
ETA: also seems possible that in scenario #2, in the period of time between when BB departed and DV returned home, if Maleah was left home by herself, she could have been injured, maybe by choking or in another fall (which given her history could have led to her death). I think this is less likely because DV would have been less likely to panic the way he obviously did.
We know she wasn't burned with the bees since she was seen on the neighbors camera on Apr 30 (bees were killed Apr 27). However, could he have taken one of those boxes somehow to use later? IDK. Some of the beehives were also thrown into a lake. There's a photo of the water here: 
