The generational chasm between our parents’ lives and the memories we preserve of them — sure, in turn, to warp and fade when passed to our children — is elegantly explored in “Little Girl Blue,” Mona Achache‘s pained, poignant docudrama cry to her female elders. In an effort to process her mother Carole’s death by suicide in 2016, the filmmaker collates an assortment of archival materials to trace the arc of a turbulent and care-starved life, leading inevitably to the time-blurred figure of Achache’s grandmother, writer and editor Monique Lange. But it’s in the gaps between tangible records that the film gets most interesting, as Marion Cotillard steps in to inhabit the Carole of her memories, the ones Achache can’t quite find on paper. 

This is hardly a novel technique, given the evolving hybridization of the documentary form, as filmmakers chase larger audiences with the narrative and aesthetic comforts of fiction. But the involvement of an Oscar-winning actor in “Little Girl Blue” never feels like a strategic ploy, not least because Achache cops to the artifice of the entire enterprise, revealing all the seams and joins of the project as she and Cotillard rehearse and workshop their recreation of Carole. Watching Cotillard mold herself to Achache’s conception of her mother — not fluently, but by tricky trial and error — underlines the malleability and fragility of memory, buffeted as it is by unreliable glimmers of the past and the distraction of present-day counterpoints. The resulting film is effective both as a raw family therapy session (albeit with only one member present), and as a prismatic study of performance and cinema as subjective conduits of reality.

Even from a less personally invested perspective, Carole Achache would be an interesting documentary subject. A writer, actor and photographer who was born into effective Left Bank intellectual royalty — Lange’s literary circles included Jean Genet and Violette Leduc, her father was celebrated science historian Jean-Jacques Salomon, her godfather was none other than William Faulkner — she never quite found her own footing in that world. Via a substantial trove of Carole’s letters, journals and diaries, Achache uncovers a dark tangle of trauma, headlined by the film’s most startling claim: that the aforementioned Genet groomed the 12-year-old Carole, culminating in her sexual assault by one of his lovers, a violation of trust compounded by Lange’s alleged complicity therein.

Achache doesn’t dwell luridly on such revelations, instead gathering them — quite literally, as her expanding collections of documents and photographs take strikingly vast physical form in a studio set fashioned as Carole’s apartment — into a kind of audiovisual psychological report, taking on ever more agonized, shadowy heft as the film follows her into adulthood. Against the sexual, political and intellectual liberation of the late 1960s, Carole is simultaneously freed and trapped once more, turning to sex work and drug use as healing and self-realization continue to elude her. 

Carole’s connections help her forge an acting career in the 1970s, with small roles in films by the likes of Costa-Gavras and Joseph Losey, though stardom never beckons. When she tries to launch a writing career, she experiences rejection, perhaps tellingly only getting a book published after Lange’s death: Her bohemian elite background is presented throughout as a burden of privilege. Only in motherhood, with Achache’s birth in 1981, does she find some semblance of stability and satisfaction, though that may be the child’s perspective, and enduring adoration for her mother, tilting the portrait. “Little Girl Blue” is especially touching as a testament to the inner lives of parents that their children never fully know, and to the torment often silently raging behind our rosiest memories.

Achache and editor Valérie Loiseleux deftly weave the film’s evidential fragments of the past — audio recordings, home movies, an avalanche of faded photographs — into a restless, flickering slideshow of recollection that often feels, however archivally rooted, emotively pulled from memory. This material thus takes on a bleary, amorphous quality that is atmospherically consistent with DP Noé Bach’s soft, low-lit lensing of the film’s dramatized portions, with the images sometimes appearing inky and tear-stained, deepening in intensity as Cotillard and her director find their way into Carole.

In a remarkably committed, empathetic performance that (in a rare coup for a nonfiction work) earned the star a Best Actress César nod, Cotillard enters proceedings as herself, chicly attired and ready to work, before stripping down to human foundations. Gradually layering herself with Carole’s physical markers — clothes, contacts, wig, jewelry — she begins by lipsyncing to recordings of the woman herself, as the film briefly mimics the experimental construct of Clio Barnard’s 2011 film “The Arbor.” But as Cotillard finds her literal voice, these self-conscious details of process fall away, and the actor’s evocation of Carole’s mounting psychic pain turns immersive and entirely upsetting. Finally, it’s by entrusting the memory of her mother to a gifted and unrelated third party that Achache finds truth.