She’s off the rails!

A woman got aboard an uptown F train, sat down, handcuffed herself to the handrail and casually proceeded to scroll through her phone, leaving hundreds of social-media users baffled — and hoping that she didn’t throw away the key.

A fellow passenger snapped a photo before getting off at 42nd Street, and submitted it to the Instagram account “New Yorkers,” which shared it this week with its 436,000 followers.

“Wanted to put this out there to the people for theories because I am f–king lost,” Leo, a 41-year-old from Brooklyn, wrote.

In just a few days, 1,000 comments poured in offering guesses and opinions.

“She doesn’t want to lose her seat,” said one.

“We’re taught to act crazier than the craziest on the subway to survive,” someone else explained.

Others made “cuffing season” puns, referring to the winter months when people want a relationship, and wondered if the unknown woman was searching for a “boo.”

Many said she was a doppelgänger of rapper Lauryn Hill, who is known to show up late to her concerts:

“Lauryn Hill, making up an excuse for being late to her next show,” joked one commenter.

Leo, a Brooklynite who gave only his first name, said he wasn’t surprised by the popularity of the photo, which he took Dec. 6 on his way to work.

“The photo had all the key elements,” he told The Post. “Celebrity look alike, commentary on the state of crime, a fashion review, a human trafficking warning.”

Some guessed the well-dressed woman was afraid of being kidnapped. Others wondered what would happen if someone grabbed her bag while she was chained to the rail.

Others said everyone should just mind their own business.

Leo, of Gravesend, liked a few of the theories: “I am still on the fence between a well-intentioned but ill-prepared drug mule, a person who was trying to put up a protective force field of crazy — as you do in New York City — and, simply, Lauryn Hill … I suppose these are not mutually exclusive.”