That scene would’ve been better if she just asked Twilight to give her the book, Twilight asks why, and then Starlight just replies “trust me”.
Starlight then simply closes the book, and explains the motive.
Having the scene play out as it did instead gives the notion “screw the rules, you’re a princess” which while I’m glad they finally use again, it still should be presented more rationally despite the fact that Starlight did so, otherwise.