My friend's sister said McGonagall was evil, and many proofs of this occurred to me when I was taking a shower the other night

It really kind of makes sense. Because there are all these suspicious circumstances, like:

1) McGonagall hanging out at the Dursleys' house after Voldemort dies. What's she doing there? WHAT IS THE DEAL? She's not waiting for Dumbledore (cause she doesn't greet him until he says hey to her first, and besides she asks him what he's doing there). And she totally tries to stop Dumbledore from leaving baby Harry with the Dursleys.

2) McGonagall doing nothing to protect the Philosopher's Stone. Three first-years have managed to find out about it, so obviously it's not as safe and secret as she thinks it is, but she doesn't even bother to check on it. She doesn't even go see whether Fluffy's still sleeping. She doesn't even send a Patronus to Dumbledore to be all, Hey, uh, these kids know about the Stone, is that cool? SKETCHY. (The Internet also thinks it's sketchy that she shows up along with Snape and Quirrell when Harry and Ron knock out the troll. Isn't she supposed to be in the dungeons with the other teachers, since that's where the troll is supposed to be?)

3) In the fifth book, she just totally lets Fudge have a dementor kiss Barty Crouch Jr. Is she that much of a failure? Seriously? She can't do Patronuses? She can't lay the smack down and be all, NO DEMENTORS IN HERE? Or is it that she doesn't want Barty Crouch to give evidence? YOU DECIDE.

4) In the sixth book, she takes Harry away to her office privately and interrogates him, with less and less friendliness, about his private lessons with Dumbledore. What's her deal? Harry's being loyal to Dumbledore's wishes and she should really do the same! Besides, this scene is faintly reminiscent of fake-Moody taking Harry away to his office in the fourth book, and strongly reminiscent of Harry's encounters with Scrimgeour. And neither of them are very nice men.

5) She wasn't in the Order the first time around. That means absolutely nothing, really, but hey, I'm just saying.

6) We've been set up to perceive her as Dumbledore's right-hand woman, but he never seems to tell her anything. Like, ever. EVER. He doesn't tell her why he's leaving Harry with the Dursleys; he sends her out of the room in the fourth book before letting Sirius reveal himself; he doesn't tell her what he's finding out about young Voldemort; he doesn't let her come hang out with him when he escapes from the Ministry. It's just a leetle bit weird, considering how right-hand-womany we're supposed to believe she is, that she's less in Dumbledore's confidence than, for instance, the Weasleys, or Snape. Or Harry, of course.

(I thought of these things in the shower last night. I am often a total genius when I am taking a shower. My brain just works better when there is water falling on my head.)

All this was suggestive, but then I read this interview with her that kinda clinched it for me. The interviewers are asking her whether Snape is evil, and she gives her customary ambiguous answer, and then this happens:

ES: I know Dumbledore likes to see the good in people but he seems trusting almost to the point of recklessness sometimes.
JKR: Yes, I would agree. I would agree.
ES: How can someone so -
JKR: Intelligent -
ES: - be so blind with regard to certain things?
JKR: Well, there is information on that to come, in seven. But I would say that I think it has been demonstrated, particularly in Books 5 and 6 that immense brainpower does not protect you from emotional mistakes, and I think Dumbledore really exemplifies that. In fact, I would tend to think that being very, very intelligent might create some problems and it has done for Dumbledore, because his wisdom has isolated him, and I think you can see that in the books, because where is his equal; where is his confidante; where is his partner? He has none of those things. He's always the one who gives; he's always the one who has the insight and has the knowledge. So I think that, while I ask the reader to accept that McGonagall is a very worthy second-in-command, she is not an equal. You have a slightly circuitous answer, but I can't get much closer than that.

Why's she talking about McGonagall? Nobody is talking about McGonagall! We are talking about Snape, woman! Are Dumbledore's willingness to believe the best of people somehow linked with McGonagall in her mind? We've never had the faintest hint that they are, in the books. Why's she talking about McGonagall?

And, okay, this is weird. She doesn't say, McGonagall is a very worthy second-in-command, but she is not an equal. She says, I ask the reader to accept, etc etc. She describes her answer as circuitous, but the only circuitous thing I perceive in that answer is her hedging about the question of McGonagall.