If this season's Xin had a theme song, I suspect it would be "Lola".
Unfortunately for Diao, when he got the proof he needed it was with a full audience.
It was never going to be easy for Diao to win over the confidence of the Feixin Unit. New strategists face a legendarily hard time when joining a new unit anyway, and then there's the fact that she's a little girl. Diao is actually lucky that Qian Lei has trailblazed for her here, because at least these farm boys have a context for a female being smart and badass - but Qian Lei won their confidence with her fighting skills, something Diao hasn't done - and that makes a huge difference. And then there's also the fact that Lei is Lei, and Diao is, well - a little girl. With Kugimiya Rie's voice.
Meng Yi makes it clear to his brother that Diao is the real thing - "the only one able to compete with her is me." the boy says, and this boy would go on to be one of the greatest strategic minds in Chinese history. But the episode takes a very interesting look at the role of the strategist in this episode. As Meng Tian points out, it takes more than strategic sense to succeed - a strategist must also have "hostility". Meng Yi explains it in terms of willingness to put the lives of men in your hands, to send them to kill and be killed - and in his case, he's never stepped on a battlefield before, and cannot truly understand the emotions involved. Diao has, of course (the razor-sharp Meng Yi professes not to know this, but clearly suspects), though she finds the feeling to be quite different now that she's stepped into her new position.
Wei general has set for the unit, and manages to move the headquarters and regroup the units scattered by his attack. This gets his attention, and he does exactly what a smart strategist would do - sets about launching an attack expressly designed to test just how good the Feixin's new strategist (it's now obvious that they have one) really is. With a force of only 1000 men and an elite army of 4000 on the attack, she's going to have to be very damn good indeed.