"At first I'm thinking, 'Oh, my goodness, I haven't done that much and I'm getting to work with Anjelica," Willis said. "But she was very sweet and helpful and just such a pleasure to work with."
In the episode airing Monday night, Willis guest stars as Bethany, a character who has fallen down what the actress calls "a slippery slope" to drugs and prostitution.
"It was fun for me," said the 20-year-old Willis. "It's something I've never really done, been able to go outside myself and play a character that was so different from myself."
Huston is returning to "Medium" as Cynthia Keener, an imprisoned private investigator who has a connection to the troubled woman played by Willis. The episode is directed by series star Patricia Arquette.
The drama holds a family connection for Willis: Glenn Gordon Caron, its executive producer, gave her father, Bruce Willis, his big break on the TV series "Moonlighting" in the 1980s.
Caron, who's known Rumer Willis since she was a baby, said he was visiting her dad in New York about six months ago when the actress dropped by.
After complimenting her on her role in the movie "The House Bunny," Caron recounted, he told her, "I probably should be looking for something for you on 'Medium.'"
He's pleased with the outcome, he said: "She really rose to the occasion. She's quite terrific in the show."
Rumer Willis considers it "a cool thing" to be able to follow in her dad's footsteps with Caron, adding, "One can only hope you do well and live up to the name."
And her father's reaction? Thrilled, she said, and that's even before the episode airs.
"My dad actually called me the other day. He'd been in a taxi cab and apparently there was an interview that that I'd done about 'Medium.' He was in the car with my stepmom (actress-model Emma Heming) and he got all excited when he saw me."
Another parent, stepdad Ashton Kutcher (married to her mom, Demi Moore), is a prominent Twitter fan. Willis said she's a dabbler compared with Kutcher, but admires the microblogging Web site.
It gives everyone a chance to be themselves, including celebrities, she said.
"It's a great place for starting a new era of people being less harsh or judgmental," she said. "You can really get to know people and everybody is just a human. Just because they have a different job doesn't make them any less a person than anybody else."
Copyright 2009 The Associated Press.