Valerie Harper is positively radiant these days. There's a sparkle in her eyes and a genuine warmth in her smile. Why not? She's defied the odds.

Early last year, Harper was told she had three months to live. A nonsmoker who had a cancerous tumor removed from her lung in 2009, she has a rare form of lung cancer that had spread to areas around her brain.

"I was supposed to be dead a year ago," says Harper, 74. "We are all terminal, let's face it. My husband, Tony, took it terribly. He said, 'That's not true. I don't accept that.' "

Despite the devastating prognosis, "I kept going. I thought it was important," says Harper, who became a TV icon in her Emmy Award-winning turn as the endearing window dresser Rhoda Morgenstern on "The Mary Tyler Moore Show" (1970-78) and her spinoff series, "Rhoda."

And she thought it was important for her fans, whom she calls her "extended" family, to know about what was happening. "People write me letters -- not just about this -- that are so loving and supportive, for years," she says. "I know there are a whole bunch of Rhoda rooters out there."

Harper has kept up an extraordinary pace since her diagnosis. She reunited with "MTM" stars Moore, Betty White, Georgia Engel and Cloris Leachman for the finale of TV Land's "Hot in Cleveland" last fall. She did "Dancing With the Stars" last season -- Harper and her partner, Tristan MacManus, were voted off after their fourth dance -- and has a quirky guest-star role in Martha Williamson's ("Touched by an Angel," "Promised Land") new series, "Signed, Sealed, Delivered," which premiered April 20 on the Hallmark Channel.

"The message of all of this is: Don't give up on your life worrying about death," Harper says, during an interview at the Hallmark Channel offices in Studio City.

Last month, Harper took to the media to clarify a magazine article that quoted her as saying, "I'm absolutely cancer free." Harper isn't "absolutely" cancer free. But she has responded well to the medicine she has taken for the past year.

"Every subsequent brain scan is less and less, and now my brain scan looks normal," she says. "It's great that it's cleared up in my brain scan, but it could be anywhere the spinal fluid is."

Long before she was cast as Rhoda, Harper was a professional dancer who appeared in the corps de ballet at the Radio City Music Hall as a teenager, as well as in the chorus of such early 1960s musicals as "Wildcat" with Lucille Ball and "Take Me Along" with Jackie Gleason and Robert Morse.

But it had been a long time since she danced when she joined "Dancing With the Stars" last fall. "I turned it down many times," she says. When the series approached Harper after her diagnosis, she told her husband, 'Why should I do it? I have cancer.' He said, 'That's why you should do it. Think of the people you will inspire.' "

She got letters of thanks, including one from a woman who wrote her, "My mom has cancer, and I can't get her off the couch. But she saw 'Dancing With the Stars' and went to dance class the next day."

Harper and MacManus have remained close and even meet for an occasional dinner. "I had such a great time working with Valerie," says MacManus. "I didn't know much about her beforehand. Generally with the show I try to get to know my partners. I was really surprised at how interested Valerie was in me, as well. There was an honesty about it. It was like we were building a relationship as well as a partnership."

"Signed, Sealed, Delivered" revolves around four civil servants who become an elite team of lost-mail detectives determined to deliver the undeliverable. The uplifting family show reunited Harper with Williamson, who has been a good friend since the actress did her first "Touched by an Angel" episode, as well as series star Eric Mabius ("Ugly Betty"), who worked with Harper in a 2001 TV movie, "Dancing on the Harvest Moon."

Harper's Theresa is the group's new, slightly eccentric supervisor. All she really wants to do is act, even though she's a postal service worker. Harper performs the life-affirming "No Time at All" from "Pippin" in the first episode and, in the second, offers sage advice to her staff on not wasting a moment of life, as Glinda in an amateur production of "The Wizard of Oz."

The role was tailored for Harper. "Valerie is somebody who would take a challenge like this and turn it into an opportunity to encourage other people," Williamson notes. "The first thing she and Tony said to me when I told them about the show was we want to use this show as an opportunity to encourage other people."

Harper also encourages everyone on the set. "Actors are usually terribly neurotic and worried about what people are thinking of them," says Mabius. "It's a breath of fresh air to be around Valerie, who wants everyone around her to succeed. She's constantly pushing people to be better than they think they can be and making sure everyone has fun."

Harper plans to keep working as long as she can. She's mulling two plays "heading toward Broadway. Maybe," she says, smiling. "There is one I really love. We'll see."