It all depends on what angle you're going to look at it. In the sense that destroying the Mirror ensured her and Zelda's people's safety, I think she did the right thing. However, from an alternate angle, she gave up her obvious love for Link (I think that she loved him anyways. I think that's a pretty common theory, but I'm not sure). So, while she did good for many, she did give up her own desires. While this was very selfless of her, she did in fact do wrong to herself. Now, while many people ascribe to the "the needs of the many outweigh the needs of the few" (myself included) it is undeniable that she did some wrong to herself. So while she may have done a greater good, she nonetheless committed a wrong. I think that her actions were very grey, and that they were meant to be that way. So I'm going to vote indifferent on this one.