Hmmm, let's analyze the evidence:
Exhibit 1: it is mosquito season, and Galadriel is a helpful person. She would not want to see another person suffer, even if it is a younger brother. Evidence points to not deliberate.
Exhibit 2: she smacks you on the BACK OF THE NECK. That appears to point away from deliberate abuse, since if one is attempting to satisfy the urge to smack another being, preferred parts tend to be a smack to the forehead, aft-head,, crown of head, possibly face, and (heading to the other polar extreme) a kick in the butt. But smacking someone on the bck of the neck seems like a waste of a good opportunity to biff someone and get away with it.
Also seems inconsistent with someone doing it on purpose, so another point for not deliberate.
However-
Exhibit 3: Galadriel is smart. She is also a writer. Therefore, she may have already taken into consideration points 1 and 2, and is counting on you not knowing that she knows that you think she doesn't know. I think. She may have deliberately skewed her freebie slap on a less-satisfying part of your precious self so you would THINK it wasn't deliberate. And then she SAID it was a mosquito instead of "oops I slipped" or "oh I thought the bunny was about to jump and I reached to grab him" or "tag" because she knew you'd accept said-supposed "mosquito" due to time of year. Where is the evidence of said mosquito? Was there a little crumpled body? Did you see it? I suspect NOT. Therefore, this evidence points to deliberately, painfully GUILTY of doing it on purpose.
Furthermore,
Exhibit 4: she is your sibling. She is also an older sibling who's had time to study you and figure out your vulnerable spots befor you could even spesk. She is also a female sibling to your male self. Not sure what that has to do with anything, but there it is. And there is overwhelming, 100% true anecdotal evidence that siblings like to torment each other. Even if they would defend each other and pummel without mercy a stranger who might try to lay a finger on their little brother or older sister or some other such combination, they will just as quickly then turn on and torment each other. Or smack you on the neck and pretend it's a mosquito. Therefore, it is further evidence that this was a purposeful act.
So there we have it. After careful deliberation, it is conclusively clear that the evidence is inconclusive. And the only unbiased witness we have is the bunny, who refuses to speak. Or possibly may have caused the mishap, if Marinea is correct. And possibly the mosquito, who is MIA. I think you may have to resign yourself to not knowing for sure. But loving your sister anyway. And by showing that love by helping rid her of mosquitos, should they appear on her precious person, as well.
opcorn: 
