Patricia seems surprised by the halfling's offer. "We're headed to Candlekeep already, so I'd be happy to mention you to Matreous if we see him. I already have a book that should gain me entry, but just in case - " here she pauses and concentrates for a moment, and then a duplicate of the halfling's book appears in her hands. "See? We should be fine, you can keep your heirloom." She tucks the duplicate book into the inside pocket of her coat with a quick motion.

Spoiler: OOC
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It's just Prestidigitation, so anybody who identifies the spell can know that "Patricia" was deceiving the halfling (and Kynos?) into thinking she had copied the book when really it's just an illusion of the object. But they can probably also tell that it wasn't done out of malice - as with the offer of dinner money, Patricia seems to be trying to politely refuse to take Breeni's treasured book.