It's not every day that a mother has to watch her golden-haired, sweet-natured teenage daughter prostitute herself for a shot of heroin. "It was very heavy," Kathy Christensen says of seeing daughter Erika's haunting performance as Michael Douglas's strung-out junkie kid in the critically acclaimed drug movie Traffic. "I had to hang on to what I know Erika is."

Which is about as far from a wasted juvenile as an 18-year-old can get. Homeschooled by Kathy, 49, a construction manager, and her father, Steven, 51, a human-resources exec (twin brothers Brando and Dane are 13, and older half brother Nick is 26), Erika, a committed Scientologist, set her sights on an acting career at age 12 and earned her G.E.D. at 16. And, for the record, says the Seattle-born teen who lives with her family in L.A., "I had never inhaled in my life!"

But pretending to smoke crack on-camera was the least of her problems: "It was strange knowing that the crew and my parents would see me doing a sex scene," she says. "But I remember sitting on the set in my boxers thinking, 'Everything else has gone great, there's no reason this wouldn't go great.' " It did. "Erika is full of raw talent," says Douglas. "She did an extraordinary job."

Her blossoming career, which included guest spots on such TV shows as The Practice and Frasier, has left Christensen little time for much elseā€”not even socializing. "I can't remember when I went on my last date," she concedes. But then, unlike her onscreen alter ego, she adds, "I've got really high standards."