Actually, for Mu Qiuniang, finding someone isn't really a big deal.
By the time she sent Murong and Li Qiqi out, she already knew the result.
But she needed to give the two disciples some training opportunities. The senior disciple, Zhan Jingshu, could already handle things independently, while Murong and Li Qiqi were still somewhat inexperienced.
As for her, she didn't have much time to waste since, as her cultivation progressed, the time for ascension was drawing near.
She needed all of them to become independent.
Basically, everyone around her was kept busy with various excuses from her, giving them plenty of training opportunities. Even those "servant" disciples sent by Sect Leader Gong Xihe from Hidden Immortal Sect couldn't escape.
