The problem is not simply knowing who sent the Valentine, but knowing what JKR’s purpose was in this episode. Is it a red herring, designed to arouse and deflect suspicion? Or a red flag, signalling something important later in the book or in a future book? Or is it something which JKR somehow thought was just obvious, and now regards as complete and intends to do no more about?
This question is difficult because we know that it is indeed a red herring. In its immediate context, the Valentine is there to give cover for Ginny’s embarrassment over seeing that Harry has Riddle’s diary. The perceptive reader (not me) can note that Ginny sees the diary and is horrified, and might work out a good deal more from that. The rest of us just see a lot of pre-teen awkwardness, and have a good laugh along the way. Without this incident, Ginny would never have seen that Harry had the diary, and we the readers would never have had a chance to penetrate the mystery.
This red herring aside, does the Valentine have any further purpose in the story? All we can say is, apparently not up until the end of GF. What we can try to do is analyse the incident from each of two alternative assumptions, and work out who would have sent it under each assumption.
Assumption 1: The Incident Is Closed
Under this assumption, JKR thought that by the end of CS, it would be obvious to readers who it was that sent the Valentine, and not a matter of any great interest. Either there is a clue she feels is obvious and conclusive, or she meant to put something in towards the end of the book, and forgot.
I would say that, under this assumption, the most likely culprits are Fred and George, but we can’t entirely rule out Ginny (in which it’s genuine and just another example of her feelings for Harry) or Draco (in which case it’s a malicious joke). My feeling is that Ginny is unlikely, because it would just make her vulnerable without actually advancing her cause with Harry, and that Draco doesn’t give the impression of being in control in the incident; he is reacting to events. Peeves is another distant possibility. Lockhart I don’t believe (I interpret the phrase ‘deliver your valentines’ to refer to those to be sent, not to be received); he has no sense of humour; he wouldn’t draw attention to Harry in this way, especially with a reference to his chief claim to fame; even a teacher as crass as Lockhart wouldn’t be sending valentines to pupils unless he meant them for real and his intentions were deeply dishonourable.
Fred and George, on the other hand, apparently go on to sing it repeatedly, suggesting that they may already have known the words (though the large crowd observing it could have contained people who memorised it, or Fred and George themselves). JKR couldn’t trail the true authorship too early or too obviously without alerting us too strongly to the importance of the Ginny-diary connection. If Assumption 1 is correct, the time to reveal it would be in the Chamber itself, via Tom Riddle’s quotes from Ginny’s entries in the diary. The point that Fred and George tend to take the credit (and blame) for their jokes is a good one, however.
Assumption 2: Red Flag/Red Herring
Under this assumption, something will come up in a later book which will give the Valentine added significance. For us fans, it’s the one we would like to be true. If it is, almost certainly the Valentine is not a joke and somebody out there has strong feelings about Harry. The significance could either be the identity of the sender, or it could be something in the words.
If the significance is in the words, I think it must be the pickled toad. Harry’s green eyes, and eye colours generally, are frequently emphasised. Have there been any significant mentions of toads? I did wonder if Neville had something to do with it for this reason, but couldn’t make anything of it; any thoughts? Pickling makes us think of Snape’s office; any possibilities there?
What about the obvious suspects? Ginny is again unlikely, (though she can’t be ruled out) as there is no new ‘flag’ or ‘herring’ involved; we already know about her feelings for Harry. She did send a singing card to Harry in PA. Hermione I think is also unlikely but not impossible. She has sent a Valentine to Lockhart, and is not about to suddenly declare, even anonymously, a hidden affection for Harry. The style of poetry, if we may call it that, is very unlike the practical Hermione, and the comparison to a toad sounds like somebody from a wizarding background.
Cho? Very doubtful; she has not yet been introduced, and not clear where it would be pointing. Draco? Again, not sure where it is leading. Riddle? No, he is inactive at this time, he can’t do anything without someone using the diary, which, of course, is in Harry’s possession.
My money, under Assumption 2, would be on Moaning Myrtle. She is developing an interest in Harry, which GF makes clear is still there. She fantasises about him (see her remarks when they emerge from the Chamber). She is resourceful and persistent, as Olive Hornby found out. Despite usually hanging round the plumbing, she is potentially in good contact with the wider school life via Nearly Headless Nick, who invited her to his party. She has an un-ghostlike resentment of being dead, which may result from the obstacle it presents to further development of a relationship with Harry.
If there had been pickled toad in the Polyjuice Potion I would have said it was a clincher; but it’s not mentioned.
This post has been a bit of a pompous Percy job (could he have sent the Valentine under the influence of the sinister Prefects Who Gained Power, surely another Malfoy plant?), but I wanted to cover the possibilities and I think it really is an open issue.
In 2005, Rowling answered this question in an interview:
MA: Did Ginny send Harry the valentine?
JKR: Yeah, bless her.
MA: Was it a Tom Riddle thing, or Ginny Weasley?
JKR: No, Ginny Weasley.
MA: Well, she got paid back for it.
JKR: [laughs] Eventually. (TLC)