"Little House" Star Alison Arngrim "Abused"

Alison Arngrim, the actor who played the angry, conniving brat Nellie Oleson on the popular 1970s TV series "Little House on the Prairie," says there's a reason she was so convincing in the role: She was a victim of childhood sex abuse.

Arngrim was 11 when she took the role of the little girl America loved to hate, and she says being able to vent her rage may have saved her sanity.

"When you live with abuse, you have a lot of rage and anger, and I had a place to actually take it and vent it as Nellie," Arngrim told The Today Show Wednesday. "It's done me so much good, I can't even describe it."

Arngrim, 48, first revealed that she was sexually abused by a family member starting at the age of 6 on Larry King in 2004. But now she says she's telling her story in all its complexity through a new book, "Confessions of a Prairie Bitch: How I Survived Nellie Oleson and Learned to Love Being Hated."

Arngrim told King that, looking back, it's clear to her that she showed all the signs of being an abused child. She was withdrawn, fell asleep in school and cried a lot. But her parents may have been in denial, she said.

As she grew older, she saw other celebrities talk publicly about their abuse, but never thought she would become one of them. But now she is a woman on a mission. She's involved with The National Association to Protect Children, an organization which lobbies for legislation aimed at protecting kids.

One in four girls and one in six boys is sexually abused. And there are an estimated 39 million survivors of childhood sexual abuse in America today, according to the Centers for Disease Control and Prevention.

Nellie, the mean girl nemesis to the show's sweet protagonist Laura Ingalls, was a girl she grew to love. "She transformed me from a shy, abused little girl afraid of her own shadow to the in-your face, outspoken, world-traveling, politically active, big-mouthed bitch I am today," Arngrim told Ann Curry. "She taught me to fight back."