I guess her using the 'square setting' and helping lead her crew, the Doctor and Donna out of a deathtrap doesn't count.
I don't consider getting out of a situation that only existed because you led a team of ill equipped and woefully ill prepared people into a situation that lead to their grisly death and imprisonment, in what is essentially the matrix, for eternity with the same group of people a success, no.
or tracking down a Weeping Angel right before it hijacked the ship. she didn't stop the thing, but she did call the Calvary
I think its worse given that shes done the same thing previously with people far better prepared with those ones, and they all died and had their corpses reanimated by aliens that would have died if they never went there in the first place.
That's two situations that would have been better off if she just left well enough alone, one of which was only in any way successfully resolved because a person she had no idea was going to be there turned up and fixed the problems she caused.
or sacrificing her life so that the Doctor would live on
I'm drawing a distinction between Melody and River at this stage because the characters in the show are, and I actually thought she was a good, if again, completely ineffectual bad guy.
Nor does her shooting up of the Silence
I'll admit, her spinning around in a circle wildly firing her gun may have had a higher chance of killing her enemies than her allies, and I had forgotten that. Its things like that though, and her delivering her 'awesome' one liner before blowing up a dalek, that just reek of the writers trying to make us like a character that they want us to like by making her so 'awesome' that we cant not like her. Doctor Who is about problems being resolved in an amusing and clever fashion. If I want to see them resolved by forced dialogue and shooting things, I'll by 24 on DVD.