Rachel Yoder knows exactly why she wrote her bestselling debut novel, Nightbitch. “After the 2016 US elections, I was in shock and I was also vibrating with anger.” Facing Donald Trump’s first term, she didn’t know what to do with all her “rage and disbelief and confusion” – especially because she was experiencing the same feelings about early motherhood.

Published in 2021, Nightbitch is a strange and unforgettable story about a sleep-deprived stay-at-home mother who, after apparently growing extra nipples, sharper canine teeth and a tail, develops an “exhilarating and magical” ability to literally become a powerful bitch.

It became a cult hit, was named one of the best books of the year by Esquire, got shortlisted for a PEN/Hemingway award – and has now been made into a film starring Amy Adams and directed by Marielle Heller.

Speaking to me over Zoom from her Iowa City home on election day in the US, Yoder says she thinks the book resonated with film-makers because “it’s a reaction to this shift in culture that has been so profound in the US – this whole movement on the right to return to traditional values and women staying home, taking care of the kids.”

When I check in with her after the election results, she says she is finding it hard to wrap her brain around why Trump was elected again. “But I guess this means it’s time to write another book.”

It didn’t surprise her that her novel found success at the same time as an election in which abortion rights were a key issue. “Women are really worried, and we’re looking for stories that empower us in some way – or that show us how to step into our power, out of this old narrative, into something new”, she says.

Nightbitch was born out of an essay the author wrote about how it had felt, using the lactation room at her workplace to pump breastmilk between meetings, while her baby cried for his mother in someone else’s arms. “I had this very animal, physical desire to be with my child.”

In the end, after nine months, she left her dream job running a literary non-profit organisation, became a stay-at-home mother and didn’t write a word until her son was three. “It was this real loss of identity: I have a kid, I’m not writing and I’m not working for the first time in my adult life. It was very discombobulating and disorienting.”

Heller became interested in turning the book into a film after Covid “really brought the gender divide, especially in domestic situations, into focus”, Yoder says. Mothers today are looking to see their experiences reflected in books and films, she thinks, while younger women are looking for “truth” and a different take on motherhood and womanhood: “something that’s a bit bolder, that channels their anger and desire for change”. For Gen X women like her, marriage and kids were a “foregone conclusion”, Yoder says. “I love that younger women are questioning it now.”

In one of the author’s favourite scenes from the movie, the mother and son sit on the curb, watching a dumpster truck collect rubbish bins. Sharing that experience with her own son is a cherished memory of hers, Yoder says, and one of the many quotidian experiences of early motherhood that is rarely deemed important enough to depict in a film. “It’s so mundane, but it took up so much of my life that I love seeing that on screen.”

Something else not often seen on screen that Yoder felt was “valuable and important” to include was menstrual blood: at one point the mother is unceremoniously depicted menstruating in the shower. “It begins to normalise the mundanities of being a woman and the realities of the female body. Menstrual blood is so ordinary for us yet still somehow visually taboo”, she says. “It’s refreshing to see it on screen and not have it framed as something shameful or revolting.”

The author is hoping men will also want to watch the film – or read the book – and that it will encourage them to “step up” for their partners. “It’s a call to communication – a call for honest and open lines of communication between partners, so that instead of falling back on expectations and old stories, we ask: ‘How do we negotiate this together?’” But she fears the film will inevitably be pigeonholed as “a movie for moms”, just as the novel is seen as “a book for women”.

While she thinks Heller did a “great job” of focusing in the film on the very realistic marital conflicts that erupt between her characters, she perceives the main conflict of the book as internal and existential: the unnamed mother is searching for a way of thinking about motherhood that works for her.

“She’s at war with all these different internalised messages that she’s carrying from girlboss culture, from traditional culture – all these messages that are at odds about how a woman and a mother should be – and she’s trying to figure out how she’s going to be.”

Since the book was published three years ago, “everything has changed” for Yoder. She is now an assistant professor for screenwriting arts at the University of Iowa. “I absolutely love working as a professor now, in large part because my schedule isn’t a typical 9-5 job. I have some flexibility in when I do my work so that I can accommodate picking my son up from school as well as grading, reading, and class prep.”

And now, when she writes screenplays herself, “people want to read them”, she says. “For the first time in my life, now, in my 40s, I feel like people are interested in hearing what I have to say.”

When I ask Yoder why she chose a dog as the animal her character would transform into, she explains she personally finds the species scary and dangerous. “It’s this wild animal we bring into our domestic space, but what happens when the wildness comes back? And I think with having a child, your wildness does come back.”

No one, she adds, ever tells you that you will go through this kind of identity crisis and second adolescence in order to learn who you are now, and adjust to your new life as a mother. “It’s presented as this completely natural thing, and you’re gonna just slide right into domesticity. And it’s like: well, maybe that doesn’t fit for me. Maybe I need to also turn into a dog.”

• Nightbitch is released in the UK on 6 December.