Spears explains her quickie Vegas marriage, why Kevin didn't leave Shar for her and more

During his one-on-one with Britney Spears on Dateline NBC Thursday night, Matt Lauer called the “sweet little girl” he first met seven years ago, when she sang “Silent Night” at the Rockefeller Center Christmas tree-lighting ceremony, “one tough cookie.”

“I don’t allow anyone to change me,” said Spears, 24, who had asked to do the interview to combat recent negative reports about her appearance, marriage and parenting skills. And combat them she did.

On the way she looks: “I still walk out of my house in rollers,” she told Lauer. “I do not care what people think.”

On life with husband Kevin Federline: “Awesome. Thank you.”

On taking 9-month-old son Sean Preston to the emergency room after he fell from his high chair: “The doctors acted really funny. I don’t want to say what they did, or what they said, but it was really bad.”

Spears cried several times during the interview, but when Lauer asked why she didn’t just walk away from her fame, she said, “I have to believe I’m here for a reason.” What is that reason? “I don’t know. I have to keep searching every day.”

Despite her fame, she insisted she wants Sean Preston to have “the most normal life for him that’s possible.”

When Lauer asked if she knew the sex of the second child she is expecting, Spears said no: “I wanted to be surprised.” She also said she wasn’t sure how far along she was, but Lauer calculated that the baby is due in September.

Spears also speculated on why she’d gone from press darling to tabloid target. She said she’d felt “a little shift” in the perception of her after she and Justin Timberlake broke up and he suggested in a video that she’d cheated.

Then came her quickie Las Vegas wedding – and annulment 55 hours later – to childhood friend Jason Alexander, which she told Lauer was an act of rebellion when she was saddled with a rigorous performance schedule. “But I have no regrets for anything I’ve ever done,” she said.

Next came her relationship with Kevin Federline, who, Lauer pointed out, left girlfriend Shar Jackson for Spears when Jackson was six months pregnant with their second child.

Spears pled ignorance: “I didn’t know until two months later. But I don’t blame him. They weren’t technically together when he came to me anyways. They were, you know, apart. But that happened with Julia Roberts too.” (Roberts began dating husband Danny Moder while he was still married to Vera Steimberg.)

“But it’s more talked about and more of an issue with me,” Spears continued. “Like, her husband was married and had kids when they first got together. But for some reason it’s like, boom! in your face when it happens with me, and it’s really none of anybody’s business.”

Lauer pointed out that Moder and Steimberg, in fact, had no children.

But Spears insisted that Federline – whom Lauer saw when he arrived at her Malibu house, putting to rest rumors that he’d moved out – is a good person. “He’s like a boy,” she said. “He cares. He cares so much. His heart is awesome. He has a really big heart, and I love that.”

Spears also told Lauer she’s a housewife at heart.” “I cook, I try to cook,” she said. “And I like to clean.” Her housekeeper comes once a week, but “she slacks a little.”

Although fans might be surprised to learn that a star worth an estimated $100 million still does her own laundry, Spears said in her Louisiana twang, “That’s who I am!”