I feel this isn't really a good reading of what she said. Ling Qi suggests in the section of text you quoted that the abandonment of the fox-blooded children is a twisted, broken reflection of the old religion (but what that religion looks like is questionable, Ling Qi didn't investigate that part). What it is saying is that Ling Qi has a means to investigate and potentially prove that adopting imperial religious practices was a mistake, something that any revivalist faction within the Diao will have been saying for centuries, as well as potentially cast the stewardship of the region into doubt.
Like as a weapon against the Diao, the information Ling Qi glimpsed with Su Ling would be enough to push for a power play among the clan if not spark an uprising against Diao rule from among their various vassals. Turning that over to the Diao with the statement that "this doesn't need to become an official matter", and the revelation that there might be other spirit bloods with divination talents, is both a threat, a peace offering, and the casual reveal that they have the hope diamond all in one.
