The problem with that is that it's a basically an apples-to-oranges difference between the two situations, because...
WARNING: spoilers below
...Annie's mother died of natural causes at a presumably old age, while Charlie obviously died very young in a sudden, extremely violent accident, one that Annie personally witnessed the aftermath of, and which essentially tore her entire world apart (although again, that's a response that partially ignores what the film already established about Annie's personality earlier), so it strains credulity that she would still have the composure to painstakingly create a model of the latter scenario, while also casually shrugging it off as just a "neutral" portrayal of the accident when her husband is (naturally) alarmed at the sight of it, like some sort of borderline sociopath. It's a response that feels like it was written by someone who's never personally interacted with another human being in their life, which is a bit of a problem when half of the film is coaching itself in the trappings of a relatable drama about a grieving family, you know?
Given that I'm pretty sure all your pontificating is born out of a single, clearly emotional watch of the film, I'm going to assume that you've forgotten that the other miniatures that she built that involved her mother were of creepy and upsetting situations in her life.
Her mother also didn't so much die "of natural causes" but had to move back in and is implied to have more or less gone insane.
Annie processes this through an art form that allows her to manipulate and control every detail of an event. This is thematically linked to the concepts of determinism and her mother's control over their entire lives from beyond the grave (an inclination for Annie that was perhaps... Hereditary...)
Similarly, she processes Charlie after a period of intense grieving. Artistic expression can be both cathartic and a form of detachment, refocus and meditation. This is clearly shown as Annie's process. She's also shown to hyper focus on her own obsessions and control (it comes up a lot throughout the film).
You're also off-base when you say this is supposed to be a relatable family drama. The entire film goes out of its way to imply the deep rot within the family and how it has poisoned them all psychologically from before the film began and before many of them were born (almost like they inherited it).
I think you'd have had a better experience if you'd watched and asked "why" Aster was doing what he was doing rather than asking yourself "why is this stupid?"
Maybe try a rewatch with an open mind and adjusted expectations will be the kind of meditative catharsis you need for this film.