After hearing Shen Qi's words, none of the court officials thought she was giving Lu Yichuan a chance to earn merit. They all believed Shen Qi was calculating.
First, she used a major battle to send Lu Yichuan out of the capital, making the internal affairs of the capital entirely under her control. No matter how much chaos Lu Yichuan created before, once he left the capital, all his previous arrangements would become worthless.
As for the young emperor... Without Lu Yichuan's support, could the young emperor even have a voice in the court?
Moreover, personally going to Beishan Pass to deal with the brutal and fierce nomads—who could guarantee that Lu Yichuan would win? Even if Lu Yichuan could defeat the nomads, with Shen Qi sitting in the capital, a slight manipulation of supplies could leave him unable to return alive.
Shen Qi, indeed, when she makes a move, it's devastating. And crucially, she's using an open strategy.