The former Hasidic woman who jumped to her death from a swanky rooftop bar Monday wrote a despondent e-mail to pals days before her suicide blasting the Jewish sect as a “cult” that “shouldn’t exist.”

Faigy Mayer, who was shunned by her Hasidic parents, described the sect as antiquated, oppressive and controlled by powerful rabbis.

She talked about how everything from Internet use to sex was rigidly regulated — and that even after leaving the faith she still felt its grip.

“I feel as though Hasidic Judaism shouldn’t exist at all,” the 30-year-old woman wrote in the missive, adding that “Thinking analytically when it comes to basic life decisions is something new to me and something I still struggle with, 5 years after leaving.”

In the long, impassioned letter sent on July 12, Mayer — who plunged 20 stories from the 230 Fifth bar in the Flatiron District — compared being Hasidic to being in a cult.

“Right now rabbis are winning. One of the characteristics of a cult is a charismatic leader. These charismatic rabbis are saying no to the internet,” she wrote.

She began by describing her upbringing, including early schooling in which married female teachers had to wear wigs to cover their hair — and then hats over their wigs. She said boys’ Yiddish studies prevented them from learning simple math.

“Hasidic boys aren’t as lucky as Hasidic girls,” Mayer wrote. “They do not know simple math such as division or fractions . . . They have only ‘Yiddish’ all day.”

She spoke about how many Hasidim are on welfare, and how those who try to run businesses have trouble because they can’t use the Internet.

Mayer described intimate relations among Hasidim as “the couple having sex with the wife wearing a bra in the complete dark (hole in the sheet, anyone?) but still producing 13 children generally throughout her lifetime.”

Mayer said rabbis are stifling any kind of fun.

“My 3 nephews . . . most fun they have is to color with crayons,” she wrote. “Basic joys American kids get on a daily basis my nephews don’t have.”

Mayer talked about her struggles being raised in a strict religious environment and said her “uneducated” mother diagnosed her as “bipolar” at age 16.

She was tormented with her decision to leave the faith and was hospitalized several times for mental health issues.

“IF PEOPLE WERE ALLOWED TO THINK, THEY WOULD NOT BE RELIGIOUS,” she wrote.

Faigy Mayer denounced Hasidic cult in letter to friend