You have to understand, it's implied from what Lash said at the end of White Night that she (and by extension Bonnie) has a great deal of information that is integral to the metaplot and can't be revealed just yet because it would make Harry's life to easy.
So instead she gets to be a genius with all the answers that is simultaneously too dumb to realize she has to hand them out until the last 3 chapters of whatever book they become relevant in.
...
Like, she has to be useless, or we don't get a story.
I think this is exactly correct. Harry has to be kept ignorant, or he cannot be the investigator-protagonist.
... Just as an example, she 99% knows all about what a starborn is, she can probably tell Harry exactly what Nick's been up to, may well have a bunch of information about what the Black Council has been up to...
I don't think it's
at all certain that Bonea knows everything Lash knew... but if she knows just
half of what the Shadow knew, that'd be a
huge trove of new data for Harry! I kind of think Lash knew she could only send part of herself forward as Bonea, and tried to curate for Harry to have access to the most-useful bits; but OTOH there's also the likelihood that there may have been too much chaos & unpredictability to the event, and Lash couldn't control things completely that way.
I'm pretty certain that Lasciel's Shadow knew
vastly less than what Lasciel herself knew! The "Shadow" is an imprint within a mortal mind: I don't think Angelic-scale knowledge
fits in there!

But, as for finding out Nic (and Anduriel's) actions/agenda: Bonea can only know what Lash knew, who can only know what Lasciel knew. And we already have seen secrets & infighting between the Denarians... I'm pretty sure there are exactly zero other Denarians who have an accurate understanding of Anduriel's plans.