I respectfully disagree. I don't think this is an issue of dumb or naive - the latter simply implies not having knowledge of something. We've all been young, dumb and naive.
But this is next-level rudeness plain and simple - I don't care if her perception was that OP paid nothing, got it free herself...doesn't matter. It. Was. A. Gift.
Everyone from age of 4 years old and up should know to simply say "thank you" for ANY gift - whether you like it, don't, can use it, cannot use it, wanted more or simply hate it.
You NEVER ask for more. If the failure to understand this basic kindergarten lesson is now considered natural for all young adults as "young and naive", lordy help us all.
By the way: I ADORE these community threads and reading everyone's responses - thanks OP! They perk up my day, give me a laugh or two. - sometimes they give me extra patience or appreciation when my own family does something to drive me nuts.