Had he approached Padma in a friendly manner, putting himself on equal footing (instead of trying to teach and impress!), and then told her pretty much the same things he ghost-whispered, it would still have likely redeemed her,
Personally, I disagree. When I imagine Harry approaching Padma with such a strategy, I see Padma reacting to his attempt to understand her with revulsion and self-justifying lies to minimize cognitive dissonance, thereby pushing her even further from being able to admit to herself the truth of what he says.
The ghost gambit works because, like an anonymous comment, she can't employ a cached thought like 'everything Harry says is evil and intended to manipulate me and false' and reject it out of hand, and she is rendered weak and uncertain in a way independent of Harry. Nor can she overrule her cognitive dissonance by focusing anger on Harry for manipulating her - because she has very strong evidence that it isn't Harry manipulating her.*
But perhaps I am too cynical.
* Yes, we know that Harry did it and that he obviously did it because of his invisibility cloak. But she doesn't know about the cloak, and given the enormous unlikelihood of Harry having such a cloak and a Time-turner, I don't think she is wrong to conclude it wasn't Harry.
[Update: and now there's a fifth discussion thread, which you should probably use in preference to this one. Later update: and a sixth -- in the discussion section, which is where these threads are living for now on. Also: tag for HP threads in the main section, and tag for HP threads in the discussion section.]
The third discussion thread is above 500 comments now, just like the others, so it's time for a new one. Predecessors: one, two, three. For anyone who's been on Mars and doesn't know what this is about: it's Eliezer's remarkable Harry Potter fanfic.
Spoiler warning and helpful suggestion (copied from those in the earlier threads):
Spoiler Warning: this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series. Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.
A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted. This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.