It is not entirely her fault, but without her tantrum that doesn't happen, so it kind of is because of her.

Which, you know, should be a good sign she's doing something fairly silly and immature. Of course she's the wronged party here, sort of, so we can cut her some slack, but when she's stooping that low herself she has little room to complain about Harry's or Ron's immaturity.

Part of the silliness, of course, is that she's causing more annoyance for herself than for Ron.

Fair enough, I didn't really fully take into account that she's only fifteen.

Ron is the one who is responsible, obviously, but if not for her it never happens, so... And I'm guessing she really wasn't supposed to tell Ron about Hermione kissing Viktor, so she really does wrong Hermione there, even if she couldn't know Ron would react like that.

Incidentally, Harry's comment about how he couldn't tell Hermione about the reason for Ron's sudden cold shoulder makes zero sense to me. No doubt she wouldn't really understand, but surely it's better than leaving her in the dark entirely. Though I suppose Ginny may have cleared it up for her, but really, Harry could and should've done that.