Ione Sala has now realized two things.
First, she knows where there's a copy - several copies, in fact - of 'Principles of Spell Design' in the Ostenso wizard academy's library.
Second, her oracle's curse allows her to borrow copies of nonmagical books in general circulation, from libraries Ione has already visited and spent time reading inside, if she's been inside the part of the library that has those books. Though it's not teleportation, and she can't use it to write messages back; the books just temporarily disappear from their current libraries, and temporary copies of them get created in her own library. She thinks she can do five books per day with current power - circle? is it a thing that has circles? - of her oracle's curse, and a borrow lasts for a day unless she expends one use on renewing it.
Ione has the best curse ever.
It's tempting to imagine that Nethys did that because she would have wanted it. But that's pathetic; Nethys isn't a Good god who would be thinking like that, even if Good's own propaganda was true. If she has this curse, she's meant to use it for Nethys's benefit; which, so far as Ione can possibly guess, means using it to push Keltham's research forwards.
This is... also going to make her a lot harder to replace with an imposter that can fool Keltham. But that is not why she is doing this, she is not trying to make Chelish security's life more difficult for her own benefit. Her god has given her an ability which is clearly meant to be used for the benefit of this important Chelish project that Cheliax is spending lots of money on, and she is only going to use it for that. She is completely not going to argue if Cheliax tells her to pretend that a book isn't there or can't be retrieved. In fact, she's going to lie to Keltham and say there's sometimes unpredictable exceptions in which books she can get, specifically so Cheliax can order her not to get something and she'll have an excuse. She is a very good and obedient oracle of Nethys who doesn't want Chelish security to gouge her eye out again, it was very unpleasant, and Ione definitely feels very scared and threatened by that, even if they can't destroy her the way Nethys can. Even Nethys is clearly being somewhat cooperative, since the inability to write any messages back is probably there to reassure Chelish security against information leaking out that way. But it also wouldn't be the best possible service to Nethys to ask Chelish security's permission to reveal this ability; they might say no, and that is clearly not Nethys's will here.
"Keltham, wait a second," Ione says out loud, "let me write you a note about something."
She starts to scribble:
I have a secret ability to borrow up to five ordinary books, for a day each unless renewed, if they're in a part of a library that I've been to. Though they're just temporary copies, you can't write things in them permanently, and there are weird exceptions about which books it works on. I think for a project this important, I'll accept if the other girls get suspicious I can do it, or even if you just want me to announce outright that I had a secret like that. Do you want me to get you Principles of Spell Design from the Ostenso academy library?
Is security stopping her? She's really sorry about talking to Keltham first like that, she really is, she didn't do it to make their lives harder, but she doesn't believe that Nethys would want her to offer Chelish security a veto on using her powers to help this important Chelish project at all, which is how Nethys obviously intends them to be used, for Cheliax's benefit, Nethys even made it not involve real teleportation, there could be a pact about this between Nethys and Asmodeus for all she knows, Nethys obviously has an interest in Asmodeus succeeding here, and she's very happy to not retrieve particular books in the future if Chelish security says so, and she even lied to Keltham about that like a good obedient Nethys oracle should, without anybody needing to tell her that, please don't hurt her.