From the exact moment I spied Susan Sarandon rubbing lemons on her naked torso through the apartment window in Atlantic City, I was in love.

Yep, me and Burt Lancaster, forever united in our voyeurism, but it isn’t quite what you think: Sure, the scene was rawly, almost excruciatingly erotic as Sarandon, utterly unaware of being observed (they don’t call them apartments for nothing), went about slowly disrobing and squeezing citrus on her flesh to slice out the proletariat stink of the oyster bar where she works.

But there was something else, something more to her seemingly solitary act of renewal — it betrayed the angelic naturalism and self-possession of a woman who, regardless of her circumstances, knows her true place on this sad, beautiful planet. For men as lost as Burt and me, such a thing is irresistible. For women, too, I imagine.

That was 1980. Sarandon turns 70 this year, and she’s never been more irresistible. In her latest film, a smart little sleeper of a dramedy called The Meddler, Sarandon plays Marnie, the mother from hell — not of the domineering Joan Crawford coat-hanger type, but rather of the smothering, telephoning, texting, neurotic variety, who turns every stray thought and fantasized catastrophe into a reason to pester her daughter.

Rose Byrne plays Marnie’s daughter Lori, a lovelorn screenwriter living in L.A. whose pinched, hangdog expression betrays the inner disquiet of unresolved grief. Both women, it turns out, are reeling from Dad’s death, though for Marnie this widowhood manifests in a frantic, cheerfully yammering do-gooderism. There is nobody she won’t give advice to or for whom she won’t open up her pocketbook; when Lori suddenly flies to New York for work, Marnie, a benevolent hurricane of misguided philanthropy, decides to bankroll the lesbian wedding of Lori’s friends.

Written and directed by Lorene Scafaria (Seeking a Friend for the End of the World), The Meddler is a sweet, funny and kindhearted film, though beneath its fuzzy exterior lurks a razor-sharp commentary on parenting, identity and the nature of loss. Byrne, who seems to specialize in a certain breed of feminist miasma, is good, as is the perpetually solid J.K. Simmons as Zipper, a retired cop whose patient attentions may or may not bring Marnie out of her not-so-silent desperation.

But, in the end, this is entirely Sarandon’s film. The woman is fearless. It’s impossible to imagine another actress working today — no, not even Meryl Streep — who could so subtly, and with such disarming complexity, portray the convolutions that occur beneath the surface of painfully forced chipperness. She can dismantle you with a smile, and a single glance can telegraph a lifetime of hurt.

A large part of Sarandon’s charm, and what is so essential to her craft, is the seeming effortlessness she exhibits, as though, when it comes to acting, she could take it or leave it — it ain’t gonna break her to do something else. This zen quality gives her a foundation, a kind of cosmic confidence, from which to move outward: She turns her own detachment into an asset.

As Marnie, a loving mother who elevates passive-aggression to an art, Sarandon has found a role that suits her perfectly, and she digs into it with an empathic joy that is totally captivating. The movie could have easily gone off the rails into saccharine schmaltz and ersatz uplift, but Sarandon turns it into something else altogether: a wise, endearing comedy that actually earns the good feelings of its final scene. (Bijou Art Cinemas)