Ashlee Simpson looks so pretty on the cover of the new Cosmo Girl -- she's almost unrecognizable! Ever since Jessica's sister got her nose fixed, her confidence has soared -- and it shows. Adding to her new boost was her recent stint as Roxie Hart in the London production Chicago. "There was a time when what people said about me could really get to me. But working on Chicago helped me come into my own," Ash tells the mag. "[Theater acting] had been a dream of mine ever since I was little, and being able to fulfill it ... was amazing. It taught me to be more comfortable with myself." What about all the haters? "I've gotten to the point where being credible with myself is more important to me than what anyone else says," she explains. "People make up stories about you, but they don't really know you. ... I'm not fazed by that anymore." As for her love life, Ashlee says that her relationship with Fall Out Boy's Pete Wentz is a source of complete joy. "He's a great sounding board and very supportive," Simpson says. "Pete and I compliment each other. We are best friends, and we encourage each other. I think that is so important in any relationship - it builds a solid foundation." She sounds pretty good, right?