"Aunt Wu, how could I take advantage of your family? If you don't want any money, then I'll go to someone else's house." Qin Xue wasn't the type to take small advantages from others. If Aunt Wu insisted on not taking money, she really wouldn't feel comfortable about it.
She did have plenty of produce in her own space, but she needed a reason to take it out. So, she planned to buy vegetables from Aunt Wu's house and then find a chance to swap them with the produce from her space. This way, her family could enjoy the superior quality of the crops from her space, which might also help improve their health.
As for whether anyone would notice something odd, Qin Xue didn't think too much about it. After all, they'd be leaving soon, and it's not like they'd eat it often anyway.