But what is perhaps most scandalous about "Madame le Rabbin," as she is often called, transcends Jewish politics. Unlike the United States, France is a staunchly secular country that expressly bans religion from public life. In violation of that long-standing separation, Horvilleur is insisting that religion should play a role in this Western society, which is struggling with religious fundamentalism, both foreign and homegrown.
"So many here have the impression that when people want to express their religion, it's just that we want halal meats or that we don't want exams on Shabbat. But it's not that at all," she said, sipping green tea in the cafe beneath her daughter's dance studio. "People are in search of a dialogue with their personal identities and how they relate to their identities as a citizen."
Somewhat distinctly, France expects its citizens to bracket their affiliations with any particular identity group in favor of "the Republic," an abstract community of equal citizens who bear no difference from one another, at least in theory. To that end, the state refuses to collect data on race, ethnicity or religion — categories that, officially, are not supposed to exist.
Horvilleur takes issue with this line, and her argument is that one can easily be French as well as something else. "I'm Jewish, yes, but I'm not just Jewish — I'm French, a woman, a mother, many things. Whenever I say that, people always tell me, 'Ah, what courage!' And that just shows you how much work there is to do."
This month, Horvilleur published a book — "1,001 Ways of Being Jewish or Muslim" — with Rachid Benzine, one of France's most prominent advocates for a liberal, progressive Islam. The book is a defense of the plurality of religious identity, and a call to reclaim religions from leaders who "favor the return of obscurantisms, an isolation from the rest of the world and a rejection — sometimes deadly — of 'others.' "
In France, where more than 200 people have been killed in the past two years in terrorist attacks linked to or inspired by the Islamic State, the question of "Islamist extremism" is a mainstay of public debate. But "obscurantism" is not the exclusive province of conservative Islam, Horvilleur has argued. French Judaism is in dire need of a liberal renewal, she insists.
"For many years in France, there has been a rise in religious orthodoxy manifested in many ways. It goes in the same direction as the increase in religious practice we can see in the Muslim world," said Alain Granat, a journalist and the founding editor of "Jewpop," a popular website devoted to encouraging liberal interpretations of Judaism.
As it has elsewhere in Europe, the ultra-Orthodox Chabad movement has been successful in France in recent years, with more than 100 centers scattered across the country.
France is home to Europe's largest Jewish community, a group that, since the age of Napoleon, has been represented by the centralized, state-
sanctioned authority of a "grand rabbi." That authority, known as the Central Consistory, is deeply rooted in the Orthodox tradition and what Horvilleur calls "an obsession with rites and exclusive rituals." She said that although the constant presence of anti-Semitic violence in France explains this desire for "separation," the emphasis on strict interpretations of Jewish law "does not make our task easier — of opening, not closing, the door."
According to Granat, France's Jewish population could be even bigger if, for instance, more-
liberal notions of Jewish identity were accepted. Although in recent years the Consistory has shown signs of changing, it still mainly adheres to Orthodox definitions of who belongs: those with Jewish mothers, or those who have formally converted to Orthodox Judaism.
There is also the perception among liberals such as Horvilleur that the Consistory follows Israel's religious right too closely. In September, for instance, the Consistory invited Shlomo Amar, Jerusalem's controversial Sephardic chief rabbi, to speak in one of the most prominent Paris synagogues. Amar had previously argued that Reform Jews "deny more than Holocaust deniers" and called homosexuality an "abomination."
"This for me was a violation of all that Franco-Judaism should stand for, as well as the Republic. Homophobia should not be allowed," Horvilleur said. Consistory officials did not respond to requests for comment.
"A majority of Jews in France — and I see this on social networks — do not feel represented at all," Granat said. "What should define a French Jew? This is a very broad question, because there are 10,000 ways to think of yourself as Jewish."
Horvilleur grew up in France in the Orthodox tradition and entered the rabbinate after stints in medicine and journalism. Although she had long been interested in Judaism and its philosophy, the idea came only after she arrived in New York in the early 2000s to study at Hebrew Union College. "I met people there who told me that the rabbinate was an option for me," she said. "At the time it seemed like a joke." To date, French Jewish authorities will not ordain women rabbis.
To American Jews, the majority of whom belong to the more liberal Reform or Conservative movements, little about her synagogue would seem surprising, Horvilleur said. She welcomes those with Jewish fathers and those who identify as LGBT, and she encourages community service in the name of Jewish values. Hers is also one of the few synagogues in France where girls are allowed to have bat mitzvahs, a coming-of-age ceremony after which a young person can fully participate in all aspects of communal life.
Horvilleur's congregation, the western Paris branch of what is officially called the Liberal Jewish Movement of France (MLJF), has about 1,200 members, she said. The movement has another synagogue of comparable size on the western side of the city. During the autumn Jewish High Holidays, the organization in recent years has had to rent massive concert halls in central Paris to accommodate all of the worshipers who register.
"The [liberal Jewish movement] has grown exponentially," said Martine Cohen, a Paris-based sociologist and expert on the history of Franco-Judaism. "There is clearly a public that doesn't march in the streets, and that isn't even visibly public. They seem to see these more liberal synagogues as the place to renew Jewish life in an intellectual and philosophical way."
"It's as if religion is a museum, or — as we say in France, a madeleine of Proust," Horvilleur said. "There's so much nostalgia for a 'pure' past that never actually existed. Our goal is to reenter into history — to say, 'We are what we are, but our texts, our beliefs, they are not locked in a box.' "