I started translating the original webnovel.
https://hidamarisoutranslations.wordpress.com/futago-no-ane-ga-miko-toshite-hikitorarete-watashi-wa-suterareta-kedo-tabun-watashi-ga-miko-de-aru/
@WhimsiCat
They don't even need to claim she's fake, the other country is openly aggressive towards the country harboring the fake miko. It's clear miko title is just another tool and not really someone with much power.
@PotatoZero : Not political power no, but real divine/mystical power yes.
The mother falling ill later on become the trigger to reveal that the sister is not a real miko, because it is impossible for it to happen if she is one.
Let's say Lerunda go around showing off her power to prove she's the real miko.
At some point the people in charge will be faced with either loyalty to their preached doctrine (come out and admit the sister is fake and abides by Lerunda's words) or their own personal power (everything until now)
Do you seriously think the people who're so used to being in power, that they'd been removing anyone who dare question if the sister is actually the miko, will just obediently give it up and follow Lerunda?
the miko brings divine benefits, but also divine punishment. The reason the boot anyone sis does not get along with is that they are afraid of upsetting her and bringing that punishment down on themselves, they are certain that sis is the miko because they used a divine oracle to locate the miko, i believe the priests fell comatose afterwards so it can not be easily re-done, and sis was the only one the priests found that matched the age.
The nation as a whole entered an age of prosperity with Lerunda's birth, which is why they checked for the existence of a miko, and they know the miko's displeasure would end that (i believe it is already gone, and the village getting the backlash worse), but I think when I skimmed some chapters it said that nations have been destroyed for displeasing/disrespecting the miko. It is kind of gard to nantain a bation if you suddenly gave no crops.
Also from that I got the "enemy" nation ends up in a slave revolt.