Almost certainly not the case in this particular situation, but aren't you also being presumptuous in assuming that the person who you're speaking to is not an exceptionally good musician? In doing so, I don't see any difference, really, in her comment and your response. I get a lot of these types of comments/conversations on my own videos, and they're very annoying. People who obviously know very little about music leave all sorts of idiotic and inflammatory comments, or, alternatively, very pseudo-intellectual ones. But if you can't argue with them based strictly on the points (or non-points, as the case may often be) that they're making, then you're no better, and you shouldn't adopt the attitude that you are, considering it seems to me as though that's a fairly large component of what you're complaining about. I mean sure, sometimes a comment might just be, "this is sh*t," or some such similar vacuity, and there's not a lot that you can do with that (in which case I don't have a problem with somebody just responding in kind), but that's the case less often than one might assume. As well, you could always come back at them with a "request" for them to explain why, at which point, if they try to give any justification for their comment, you can come back at their actual argument. But honestly, posting this thread reeks of, "look at me, I think I won an internet argument," so it's fairly petty and self-congratulatory in not entirely-dissimilar ways from that which you're whining about. You really weren't arguing with any of the points that the person made or forming any actual argument, so I don't think that you should come at this with the attitude that you "know how to argue" and the other person doesn't.
Topic: Ah, YouTube.