Although leaving wasn't necessarily a bad thing, without Zhou Fanghua's outburst, she wouldn't have been so determined. It was Zhou Fanghua's troublemaking that made her decide to seize the opportunity to entirely sever ties with Qiu Yiming.
Zhou Fanghua likely made such an unreasonable demand because she guessed that after the rupture between the Qiu Family and the Fang Family, there was a concern they would wholly align with General Song. Moreover, it was intended to ensure Qiu Yiming would give up on her completely. And with their limited manpower, survival outside the Safe Zone was bound to be perilously slim.
As a mother, Zhou Fanghua's swift change of mind in devising such a plan was admirable, albeit excessively selfish and cruel!
While pondering silently, Fang Yuxin watched Chen Qiao and his five companions, waiting for their answer. She specifically raised this question to see their response and whether they were willing to take the risk and follow her.