Okay..I'm kinda lost though.. Why did they take Maomao as hostage again????

Cuz she figured out why babies kept dying i think

Basically she was too smart for her own good. She figured out that the Shi clan had something to do with the suspicious events surrounding the consorts and their pregnancy. Sui Rei and her little sister Lou Lan didn’t want to kill MaoMao despite her knowing the secret, so they kidnapped her instead

Ooohhh I see,,, thanks!!!