Koala knew the evils of the world, she had endured the worst it had to offer; she didn't think it would get worse, but fate proved her wrong - the love of her life, her partner in crime, had been brutally beaten at the Reverie - then sold into slavery by the Celestial Dragons. Now, Koala must overcome her trauma if she wants to get Sabo out before it's too late.
*Basically, it's my theory for what happened at the Reverie, since Oda is intent on keeping us in suspense.
Disclaimer: Not mine, I do not own One Piece.