Valerie Harper, who is only 5 feet 4 inches tall, but big in talent, goes toe-to-toe with 6 feet 8-1/2 inches tall Brad Garrett, playing his mom on an episode of "'Til Death."

"They just said, 'Do you want to play his mom?' and I jumped at it, because I love Brad," Valerie tells ET. "I am going to be a Floridian mom retiree. They want a different mom than Doris Roberts, who was so brilliant on 'Raymond.'"

In her role as a Boca Raton senior citizen, the former "Rhoda" star sports a curly hairdo, matching coral nail and toenail polish and -- vanity aside -- painted-on wrinkles to age her.

"There is a look to Boca Raton and we are trying to get it," she says. Then she jokes, "Who is her hair dresser? Take them out and shoot them."

In the episode, Eddie (Garrett) and Joy (Joely Fisher) pay a visit to his parents in Florida, where Eddie discovers that they are planning to divorce in order to qualify for medical insurance. Eddie balks at the idea and tries to convince his mother that it's a bad decision to put his father (Jerry Adler) back on the market.

America fell in love with Valerie on "The Mary Tyler Moore Show," and she has continued to work ever since. She attributes the longevity of her career to luck and the success of the hit comedy: "I think it is also partly because the show never disappeared. It was a great show and it is show-business history now."

The "'Til Death" episode guest starring Valerie Harper airs Christmas Day at 8:30 p.m. on FOX. It is part of a "'Til Death" marathon from 8 to 10 p.m.