Tulea, a white Bichon-like dog, is never very far from her 71-year-old mistress - part confidante, part wiggly joy, part security blanket.
How inseparable are they? Fonda, making her first foray on Broadway in 46 years, found out the hard way. She was recently bowing to a rapturous audience during a curtain call when she happened to look down.
"I saw, through my legs, this white thing and I thought, 'That's not what I think it is!' And then I heard the click-click-click of her little nails on the stage," she says.
The little dog had escaped from her backstage handler, wandered out to the delight of theatergoers, and turned into a complete ham.
"She knows what the applause means," Fonda says with a smile. "She knows that means that it's over and that we're going to be reunited. She came looking for me."
Tulea isn't the only one unleashed these days. Fonda, in what she calls the "second scene of her third act," has thrown herself into stage work with characteristic glee - no surprise for a woman who doesn't do things halfway.
"I never thought the day would come that I would look forward to being on the stage every night," she says. "It's scary to some people and I would have thought it was scary, but it's not."
In a recent interview, she fights off a late winter cold with antibiotics and tea as she discusses her newfound love of the Internet, the legacy of her father and the Vietnam war protesters who continue to hate her.
In writer-director Moises Kaufman's play "33 Variations," Fonda plays an ailing musicologist desperate to discover why her hero, Ludwig van Beethoven, spent so much time at the end of his life obsessing over a third-rate waltz. Though suffering from amoyotrophic lateral sclerosis - or Lou Gehrig's disease - Fonda's character relocates to Germany to find the answer in Beethoven's archive, further straining her relationship with her daughter.
"I needed an actor who had a strong emotional life and also a great mind. I found a woman who had both," says Kaufman, whose other works include "Gross Indecency: The Three Trials of Oscar Wilde" and "The Laramie Project."
Kaufman picked the perfect time to lure Fonda back on stage. His script arrived just as she was writing a book about aging, exploring why so many great artists did their best work late in life.
"It moves me that I'm able to have this opportunity to do this particular play with this particular message," she says. "The membranes between life and death and past and present are very thin in the play, which I think is the way life is."
Fonda, who won an Academy Award in 1971 for playing a prostitute in "Klute" and another in 1978 for the anti-war war drama "Coming Home," was last seen on Broadway in a 1963 production of "Strange Interlude."
This time, she had to tone her natural acting inclinations. Since her character is tightly wound, Fonda acknowledges her ego has been tested by having to pull back. "My tendency is to be emotional, maybe because I want to be liked or something," she says. "Emotion is very easy for me. So I have to be careful to not overdo it."
That's not as easy as it sounds for a woman who commits as strongly as Fonda, whether it's acting, activism, fitness or now as a high-tech convert.
Fonda is documenting her New York adventures online, even though she only started Googling last summer. She now Tweets and blogs virtually every day - sometimes even during intermissions - with observations about acting, New York, Tulea and aging. Fans can post their reactions.
She acknowledges flubbed lines and self-doubt. Some entries are often raw and heartbreaking, as when she confessed on Jan. 15: "I am old. I am matronly."
"I'm getting immediacy from the theater, which is new - it's been 46 years," she explains during the interview. "And from the bloggosphere: instant feedback. Isn't that fascinating?"
That ability to commit fully, to just go for it, was something Kaufman got to know firsthand when he met with the actress for the first time and pitched his play. They shared dinner and then, instead of the usual I'll-get-back-to-you posturing, Fonda signed on immediately with a handshake.
"She's a testament that passion conquers everything," he says. "She hasn't lost that sense of wonder. I think that accounts for so much of her energy, so much of her passion."
Returning to New York after all these years away - her base now is in Atlanta - has offered Fonda a chance to reconnect with her father, the late towering actor Henry Fonda, who himself was often distant with his kids.
"I feel him very, very present," she says, vividly recalling being driven through Times Square when she was 10 to see her dad in a performance of "Mister Roberts."
"He loved the theater so much. He didn't talk with joy about his professional work much except for the theater," she says. Her only regret, she adds, is that he never saw her in "a strong play."
The past has also lingered for Fonda in a less pleasant way. Before a recent performance, a small group of Vietnam veterans gathered outside her theater to protest the woman they still call "Hanoi Jane."
Fonda got that nickname for her anti-war work and an ill-fated 1972 trip to North Vietnam, where she was photographed smiling atop an anti-aircraft battery. She's since apologized many times and the protests now don't faze her a bit.
"That war was such a deep psychic wound for everyone, including the people who weren't involved. There are those who need to blame somebody and they can't blame the people who should be blamed. I'm a convenient lightning rod," she says.
The play is Fonda's latest step out of her semiretirement, following roles in the films "Georgia Rule" in 2007 and "Monster-in-Law" in 2005.
What she wants to do next - other than finish her book - is still up in the air, but right now she's enjoying her return to the stage.
With Tulea, her blogging and many well-wishers, loneliness has been staved off. She also imagines someone else is pushing her on: her father. "It's a soul that I feel is present - is looking down and is smiling, is very happy for me and is rooting me on."
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