In Chapter 15, Zelretch mentions that his intervention into Remnant's state of affairs began about a year or so ago (by that point in the fic, a handful of months before the start of the Beacon semester and Shirou's arrival on Remnant), when he talked to a few people and showed them the possible repercussions of their decisions. He states that he singled out relatively small people who would not be important from a big-picture perspective or have direct influence on events, and that Ozpin did not personally know any of them. Zelretch even specifically said, "It's always so interesting to see how differently people behave when they are truly aware of what their actions might lead to." One of the people Zelretch showed potential futures to may have been Blake - she fits the bill as someone who is relatively small from the big-picture perspective, has no direct influence over events (she was never in position to control the White Fang before she left), and who Ozpin does not personally know (since she never comes to Beacon). This would also explain why she left the White Fang in a much less dramatic fashion than in canon RWBY. Her abrupt and unexplained disappearance from the White Fang in Heroes, Dreams, and Destiny left Adam in a confused state of denial, and he continued to search for her to the best of his ability, hoping that she was simply lost and would eventually find her way back. Contrast this with canon RWBY - where she explicitly and openly abandoned Adam and the White Fang, driving him into a betrayed rage - and one explanation (obviously informed by wild speculation, but still!) is that, because of what Zelretch showed Blake, she chose her current course of action as an anonymous informant acting against the White Fang. Since she didn't go to Beacon, she isn't publicly trace-able and Adam has no idea where she is, so he would have no reason to specifically target Vale, Beacon Academy, or any of its students. As a convenient bonus, her spot in Beacon was left open for Shirou, whose vastly superior combat skills and potential, penchant for heroism, and proclivity for directly defending others (as opposed to the approach Blake took after the Fall of Beacon) make him a better option for the war against Salem.