Fair enough, but when you were in college, would you have fallen for a Secret Admirer note? Perhaps that's why I don't think this prank is so terrible, it's not funny, but I would be pretty suspicions of any anonymous notes, not assuming that some person was really out there secretly admiring me. If I didn't know it was a joke straight off, I'd actually be really creeped out if I thought it was real.
honestly, I think that kind of justiification is pretty much standard for people who condon or practice bullying behavior. This is a grad class, not a frat house. If the best justification you can come up with is "she probably hasn't reached the level of actual heartbreak" then it is time to get out of the pranking business. I don't agree. Pranking people is entirely different than bullying them. Pranking can be a form of team-building and a way to lighten up and take a minute to laugh. I've pranked and been pranked in both Grad School and in the workplace. Grad school is tough, if students want to blow off some steam with a prank, more power to them. Although I don't think this particular prank was all funny, I didn't see it as anything that would devastate the girl.
Op has not indicated in any way that prnaking is standard practice here. I would hope that in an academic setting that would not be the case. If people want to hang out and pull that garbage on their own friends, on their own time - it seems incredibly juvenile but it is their call. This is not the time or place for pranking even if you think it is the highest for of entertainment.
As someone who had a really hard time making friends and dating in college discovering someone liked me would have made my day. Discovering later that that was all a lie and not only did someone not like but a bunch of people were laughing at me behind my back would have devastated me. Pranks are only funny if the entire group finds they are funny. It doesn't even sound like the people pulling the prank are her friends. Just a group of people who don't like her and are going to go ahead and show her that.
Probably - yes I would have fallen for the Secret Admirer note.
The OP said that the "the prank puller doesn't like her", which I took to mean in general, but I guess she could have meant "like" like. But I really am trying to understand how the goal of this particular prank isn't to embarass the person. And if that is the goal - regardless of if you think the person SHOULD have fallen for it - then it is mean. Plus the OP said that the girl had fallen for it "hook, line and sinker".
ETA: I could totally see someone thinking that the whole secret admirer thing was "romantic", not creepy. Not saying that would be necessarily be my response, but I don't think that is an out there idea.