FE10 in a nutshell

seen from Türkiye
seen from United States
seen from United Kingdom
seen from Türkiye
seen from Russia
seen from Maldives
seen from France
seen from United States

seen from United Kingdom
seen from United Kingdom
seen from United Kingdom
seen from Spain

seen from United States

seen from Poland

seen from United Kingdom
seen from Romania

seen from Germany
seen from United States

seen from United States
seen from Canada
FE10 in a nutshell
mickey being branded creates incentive for her parents to get rid of her and pretend she died during/shortly after birth due to normal infant mortality reasons both because of general "branded bad" sentiment and how a branded child calls into doubt the legitimacy/'purity' of the apostle's bloodline in a country where being ('purebred') beorc is super important, maybe? not super familiar with her early life and i'd be putting my bets on "devs didn't think this through enough" anyway, but i think you can kinda "that's right, the square hole" it with this
mickey being branded creates incentive for her parents to get rid of her and pretend she died during/shortly after birth due to normal infant mortality reasons both because of general "branded bad" sentiment and how a branded child calls into doubt the legitimacy/'purity' of the apostle's bloodline in a country where being ('purebred') beorc is super important, maybe?
That could have been a reason...
If Grandma Misaha wasn't around, alive and kicking, and had the brand - just like every apostle before her!
While it might not have been common, Misaha's kid (Miccy's mom or dad) couldn't ignore how young their mother appeared to be - just like the other apostles who also had a non beorc long life* - and maybe knew about the strange tatoo she had, if they understood what it was and what it meant about the Imperial line, they wouldn't snuff bby!Miccy out, but see this mark as a sign she's a true descendant of the line!
The supposed plot is supposed to go : Grandma Misaha made some decree stuff wanting to emancipate Laguz + Lekain and pals weren't happy -> Misaha met Lehran and said she wanted to reveal the truth about her identity to the world -> she was assassinated alongside Miccy (who was or not a baby at that time).
Then, her death was used to blame herons and an angry mob took revenge against them - but somehow, the angry mob's anger wasn't fueled by the death of Begion's beloved empress/apostle + her infant granddaughter, just the death of the apostle?
No one ever mentionned the infant granddaughter? Not Lekain, not Begnion random n°77, not even Lehran?
Also, infant mortality or not, if Begnion gets an imperial heir the news is going to spread, especially for a line that is, as you said, as attached as they are about their special bloodline.
Misaha's daughter - supposedly the next in line for the throne if anything happens to her - is pregnant?
The hereditary line is secured, people can sleep peacefully, the Empire isn't going to be wrecked if anything happens to the current Empress, since the dynasty is secured.
The birth of a heir is an important thing, not something supposed to be confined between the walls of a palace.
And if Misaha didn't get a daughter but a son, it's more or less the same thing : Misaha's line will continue, with the added bonus that this time it continues through a girl, so this girl, when she will be older, will become the next Empress.
And yet, no one mentions how the story pushed by the Senate was how the heron tribe tried to wipe Begnion's imperial line - killing the beloved empresses/apostle AND her future successor - nope, nothing.
*It's even wilder when you consider the larger plot : Brandeds are supposedly shunned by people around, and yet, the Begnion Apostles/Empresses- bar the mark they hide - have every attribute of Brandeds and definitely don't live in the shadows, if they're Empresses !
Maybe they bullshited some "blessed by the goddess" lie while hiding the truth, but they also had strange abilities like "receiving revelations" about the future, like crops and what not... Everything that doesn't scream "regular beorc joe" and yet, it was never... frown upon? The Senate never knew in the 600 years Begnion existed how the apostles have kickass tatoos on their hands? Nor made the link between Brandeds, long lives and strange abilities? I mean, if a heron branded's lifespan is equal to 1,6 to 2 times that of a regular Beorc, we're talking about people routinely looking young while they are over 60 and growing old to 120-130 easily!
Which makes the plot even wonkier all things considered : let Sanaki live in ignorance but come on, not even one "older" Begnion character mentionning how Miccy has the same name as the apostle's long dead sister, or how her powers and predictions - and adoration from Daein's people - are oddly reminiscent of the kind of abilities the former apostles/Empresses had before Sanaki? Hell, Numida didn't put 1+1=2 regarding Miccy ? Neither did Lekain?