disclaimer: This is all my opinion, ofc
I think it's all BS.
That doesn't fit with the official reason, the contractual problems with her parents family, that is actually more plausible.
If the girl went through all the trouble to go to MM auditions, then stay as KSS, later be in a group which would surely debut (it was a no-brainer), then why would she feel insecure with her singing and then just quit? She was auditioning for an idol group, not an artist one.
Sorry, but I can't take her seriously...
Anyway, I hope she is happy now, and that she can meet her objectives. She's still young, so she can accomplish a lot. Good luck Aina.