This situation has ended happily for all concerned. Student left a wealth of additional materials (none of them bombs) in my mailbox, with sticky notes explaining each one. One of the top notes contained the sentence, "I apologize for getting so upset." When I emailed her to tell her that everything checked out and I was signing off on her requirement, she sent me a very gracious message back.
(But I told her I'd hold onto her notebook for her, so she'll have to come by my office to pick it up. I want to see what this girl looks like!)