Lu Jiao didn't want Qi Lei to see the surgery tomorrow. This was because, for Xie Yunjin's surgery, she needed to use anesthesia and antibiotics. Those were not drugs she wanted Qi Lei to see.
She didn't have a big pile of those medicines in her space. If she uses them up, she'll need to figure out a way to get more.
Lu Jiao said to Qi Lei, "Tomorrow's surgery is very bloody. It's not suitable for a beginner to observe. You can start observing when I do smaller-scale surgeries. You're new and you need to ease into it. The surgery is important tomorrow - what if you pass out while I'm operating? That would endanger my husband."
Lu Jiao's statement was logical. Many people could not handle situations that bloody. If something did happen, it would negatively impact Xie Yunjin and she didn't want to risk it.
