Hermione. A Slytherin. You have got to be kidding me. There is no House she is less suited too. OK, so she's got some ambition, but there is no way she would have survived in the House of Snakes. She is way too much of a know-it-all for that.
Honestly, I think Ravenclaw would have wanted to kill her too. I mean, constantly being told she is right without wanting to listen to anyone else. I don't think Ravenclaws who like their knowledge too much would like that either.
I digress though. Slytherin. What cunning does she have? And can you picture her in the same dorm as Draco Malfoy for seven years. It would be a blood bath. The only question is who would win. Draco's got the back-up, but Hermione's got a nice right hook that, with some work, might break his nose. Of course. Lucius would probably try to get her expelled for that. I guess my money has to go on Draco winning, even if he doesn't win on his own merit.
That is what makes Draco way more Slytherin than Hermione could ever be though. Cunning by definition is having or showing skill in achieving one's ends by deceit or evasion. That isn't Hermione at all. She would run head first in to whatever goal she wants to obtain and bulldoze right over anyone in her path. A Slytherin meets their goals far more subtly.
Hermione so doesn't belong with the snakes, not because of her being Muggleborn, but because she doesn't know how to do anything sneakily. Add that into her know-it-all attitude and I'd give her a week before someone tries to smother her in her sleep.
Hermione does not belong as a snake. You can't convince me otherwise. Keep her in the Lion's den where I won't someone won't want to kill her. For my our own sanity. Please, for the love of Merlin, don't do it!