Most people have guiding principles. One of mine has always been: What would Rhoda Morgenstern do?

Rhoda has been on my mind a lot the last week after the actress who so indelibly portrayed her, Valerie Harper, announced she has inoperable brain cancer and possibly only three months to live.

Like certain women of my generation, I owe much to Harper and her alter ego. When she first appeared in 1970 in the iconic “The Mary Tyler Moore Show,” Rhoda was as unique as the concept behind this show about a single, career-minded woman (Mary Richards) and the memorable characters that imbued her life. As the feisty, warm-hearted, New York Jewish transplant best friend and upstairs neighbor, Rhoda was never at a loss to crack wisely on matters of some consternation, including dating, diets and long-suffering mothers.

She made girls like me laugh uproariously on Saturday night the second she entered Mary’s swanky apartment (poor Rhoda lived in the attic where she hung her clothes on a coat rack, for goodness sake) bellowing, in her broad Bronx accent, Hey, Maaarrre!”

 Rhoda may have been conceived as a sidekick to TV news producer Mary, who was supposedly prettier, thinner and sweet to a fault (her only failing, it seemed, was throwing bad parties). But to me, and I am sure I am not alone here, window-dresser Rhoda was more like the rest of us, trying to do the best with the deck we were dealt. She sometimes wore flowing kaftans and tied scarves around her head, but she exuded a bohemian style that was enviable.

She wasn’t afraid to stand up to people who belittled her such as Phyllis Lindstrom, played by Cloris Leachman, or to be adored by Phyllis’ daughter Bess who called her “Aunt Rhoda,” much to Phyllis’ chagrin. Rhoda even had a way of making Mary’s crusty, hard-nosed boss Lou Grant (the singular Ed Asner) feel comfortable, as if the two were long-lost pals. Rhoda called him “Lou,” while the typically deferential Mary called him “Mr. Grant.”

Is it any wonder that Rhoda, oozing individuality, self-confidence, style and sass, became a heroine us Jewish girls could embrace? Sidekick my tuchus; Rhoda was the real deal. So beloved was she that after years of second banana, she earned her own spin-off aptly named “Rhoda.”

True, she was plagued by some of the stereotypes that have taunted Jewish women throughout the ages. Her hair was dark and curly, her humor self-deprecating. Also, too, were periodic visits by an overbearing mother (Nancy Walker) quick to cite Rhoda’s shortcomings while heaping on the guilt.

Yet Rhoda, the anti-Jewish princess if ever there was one, showed us how to defuse the most obstinate of mothers with laughter and love — not exactly a bad lesson in human relations. (A great irony is that Harper isn’t Jewish, nor was the late Walker, yet both were often mistaken as such. In fact, Harper was so good at playing Jewish she was later cast as Golda Meir in the national touring production of “Golda’s Balcony,” then starred in the film version.)

Upon hearing about Harper’s illness my heart began to ache, not just for her and those she loves but for all of us who love her, too. Then I thought about my guiding principle: What would Rhoda Morgenstern do?

Harper, 73, must have read the minds of fans like me, for in explaining about her diagnosis in People magazine, she said,  “I know a lot of you feel like you know me, that you are part of the Morgenstern family, and I feel I know you, too, and so I owe you the truth at the same time as everybody else.”

In the same interview, she joked about already living beyond her “expiration date” since the onset of her symptoms started eight months ago. Then she glibly remarked: “I have a fighting chance until I’m gone.”

With her same wry wisdom, in appearing on the TV talk show “The Doctors,” she added, “More than anything, I’m living in the moment. I really want Americans and all of us to be less afraid of death. And know that it’s a passage. But don’t go to the funeral before the day of the funeral.”

Live in the moment. Enjoy each day to the fullest. Give yourself room to grieve but don’t let it consume you. These are all the things I am sure Rhoda would say. They just happened to come out of Valerie Harper’s mouth.

As I see it, both are a long way from their expiration dates.