I think I'd disagree with that. While there's no way to definitively know at this point, I don't think it's that unlikely that Evelyn had died in some sort of accident.
MB's attempt to cover up the death for several months is definitely suspicious (and probably indicates that she had some role in her death, whether it was intentional or some sort of mistake), but it makes sense considering her background. Her mother was basically a career criminal, and whatever interactions she witnessed with law enforcement were obviously not positive. It's likely she was discouraged from calling the police regularly by her parents. Adding on that she's barely an adult and "if you run away from consequences, they'll stop following you eventually" seems to be the Boswell family motto, I can see MB trying to hide Evelyn after finding that she died while she was temporarily wasn't watching (something like choking or getting into drugs). It's definitely not a good thing, and MB definitely has some responsibility for her child's death, but I can understand why she would attempt to keep what happened a secret even if it wasn't a murder.
JMO
I get your points and it makes me think about the child death/murder cases we see here.
Some of them are due to neglect in some way, for example, a child becomes ill/chokes/suffocates and the caregiver doesn't seek medical help because they are afraid the child will be taken away by CPS. To us it makes no sense as a dead child is way worse than losing them to CPS yet we see that claim over and over. Is it the truth? Sometimes we never find out but if it is true then we see a clueless caregiver who underestimates the illness.
More often we see the excuse of the caregiver's fear of getting into trouble with LE. IMO that rings truer and points to a lack of focus on the child.
This is common in cases where the child was injured by a caregiver, be it parent or a boyfriend/girlfriend left in charge to babysit. Injuring a child through a violent act isn't an accident no matter how the suspect tries to play it and the usual excuse is they "fell," resulting in a fatal injury and instead of calling 911 they let the child succumb to their injuries.
Then there's the accidental ingesting of drugs left laying around. Or dosing a child to "keep them quiet/make them sleep," and accidentally overdosing them. We've seen that too and it's usually only found during autopsy.
So yeah, Evelyn's death could have been an "accident" but for now we don't have information on others who were around her during her last days so I'm not quite ready to put it at the top of the list.
We also don't know how important Evelyn was to MB and IMO that is a key piece of information. For example I'm sure CA loved little Caylee but that didn't stop her from putting her own desires to party and be free over her child's well being.
I agree that MB's background probably includes distrust of LE and while that may have played a part in her not disclosing Evelyn's "disappearance" still, it's hard to understand why she agreed to numerous interviews other than to conclude she somehow enjoyed the attention. That doesn't jibe with a grieving mother. All MOO.