The Crossroads star is preparing to star in Manson Girls, a film focusing on the lives of the convicted murderer's female followers, and she has been given the unique opportunity of choosing between two key parts - serial killer Susan 'Sadie' Atkins and longtime cult member Sandra 'Blue' Good.
Manning admits she's torn between the roles because they're both challenging - but only one is truly Oscar worthy.
She tells WENN, "We haven't filmed it but I'm signed on. I can choose between two roles right now. One of them is Sadie Atkins which is the obvious part because of typecasting. I'm much more sophisticated than I get credit for and I'm much more well read and educated.
"But I've also had the opportunity to play Sandra 'Blue' Good who is still alive and she still follows Manson and she's crazy. She was the most educated of all the women that fell into this cult and she was never part of any of the murders and was pregnant during the early days of the family. She's not a part I would normally get to play but if I want to win an Oscar, which is my intention, I want the part that will stand out and that's Sadie Atkins."
And Manning is determined to draw the attention of Academy voters, with whichever role she chooses, after being snubbed in 2005.
She says, "I feel like I should have been nominated for Hustle & Flow to be honest and a lot of people feel that way, but that's fine and it wasn't my time... I'm one part away from winning an Oscar, if it's the right part, and that could be playing Sadie Atkins."
But there's one aspect of the Manson Girls project she's a little apprehensive about: "There are people who don't like her (Atkins) and what she really did in real life and I don't know if I want to sign up for that potential abuse that could come my way from people that are horrified from the murders she committed of innocent people. So I'm torn between what part do I play. It's a good problem to have!"
Manson is serving a life prison sentence after co-ordinating a killing spree in the late 1960s as the leader of the Manson Family.