Zhuo Yinzhu was indeed a person of the Second Prince.
Earlier on, she mentioned another source of support to Miao Wuxie, which referred to the Second Prince.
When the Zhuo family met with disaster, the Second Prince saw everything, and he was also aware of the Third Prince's infatuation with Zhuo Yinzhu. So he guessed that the Third Prince would probably send someone to rescue Zhuo Yinzhu, and he sent people as well.
It just so happened that a flash flood occurred, and Zhuo Yinzhu was swept away by the floodwaters. It was the Second Prince's men who saved her.
He saved Zhuo Yinzhu not just to keep an eye on the Third Prince, but before that, he didn't know that the Third Prince and Consort Jing Pin were the Emperor's favorites. He simply wanted to manipulate events from behind the scenes, keeping everything under his control.
Unexpectedly, fortune is fickle, and hence, Zhuo Yinzhu became much more useful.
