She not only told Sinclair, "This is all we have" she added, "It isn't much". The Minbari certainly would not be giving the Humans any information on Vorlon technology at that early stage. I was probably basic data like the exact location of the Vorlon Homeworld, a sanitized chronology of Vorlon/Minbari contacts, more detailed information on their atmosphere, the externals of their encounter suits, etc. Some of the files were probably filled with legends and theories about the Vorlons collected from other species. The Humans themselves knew next to nothing about the Vorlons ("We have files, big ones. They're mostly filled with empty pages.") Any relatively harmless data that Delenn could slip Sinclair would be more than they already had, which genuinely helps him, and also gives him one more reason to like and trust her. At this stage (2257) Delenn is still more Satai than she is Sinclair's friend.
Despite their claims to the contrary and their own self-dellusion, the Minbari lie all the time, often by omission (which Dukhat condemmed as worse than an ordinary lie.) Thus they don't warn anyone about the Shadows, refuse to confirm G'Kar's suspicions, mislead Sheridan about Anna's fate, etc. As long as they think they are doing so "for a higher purpose", the Minbari can lie with the best of them, and rationalize later.
Regards,
Joe