Display Morethere are multiple options:
- physical health issues - injury which needed surgery, and physical therapy
- mental health issues
- something could happen in family, example: death of parent
other factors to consider:
- she wants to finish at least some part of school
- After what happened with Treasure YG realized they could rather debut her solo
- also the reports are weird some saying she left company, some saying she just won't debut in group, overal weirdness
Well if YG is telling the truth, aside from physical and mental health issues, she could also be suffering from a disease (e.g. cancer *I hope not though*) that requires treatment for a long time or there was a better offer from another company.
It is also possible that YG might have discovered something from her that could become a problem in the future. After all, it's not like an entertainment can publicly say the real reason even if it is a trainee/idol's fault.