How did Rebeccah Bush nab the part of Brady Bunch mom Florence Henderson for the upcoming NBC movie Growing Up Brady? By showing up at her audition in a vintage 1970s outfit!

"I think they were in shock," the actress recalls of her audition with director Richard Colla and ex-Brady Bunch star Barry Williams. "I don't really think they expected anyone to come in fully dressed as Florence Henderson. I bought a wig, I got a little dress, little sandals. Oh, the looks I got on the freeway!"

It turns out the Mississippi native was the only actress who showed up for the audition in costume. "They just burst out laughing and I thought, 'Oh God, I've completely made a huge mistake. This is never going to work. They think I'm a freak,' " she tells TV Guide Channel. "Then I got the role."

Of course, her winning outfit was accompanied by a winning résumé: The actress has appeared on E.R., Frasier, Matlock, Jake and the Fatman and countless other TV shows. She launched her career playing a prostitute opposite Harvey Keitel in The Men's Club.

"I don't think my dad particularly cared for me doing hooker parts right away," she says. "He called up and said, 'Honey, I really want to know what you're wearin' out there, because I don't understand how you're getting all these hooker parts.' "

Bush says she enjoyed working with Williams, whose Growing Up Brady memoirs is the basis for the latest Brady biopic (Sunday, 9 pm/ET). "As a young girl, I had an amazing crush on Greg Brady," she says. "So it was really fun in that way just to be on the set and you're like, 'My God! It's Greg Brady!' "