The “serial stowaway”, Marilyn Hartman, has been beaten up inside a Chicago jail.

Ms Hartman is currently serving time in Cook County Jail for violating her probation.

CBS 2 reports that she was assaulted on Tuesday and that the offending inmate may have been having some kind of mental health episode at the time.

The inmate repeatedly struck both Ms Hartman’s head and another inmate’s against a number of hard surfaces. They were evaluated by medical staff at Cermak Hospital and found to be uninjured.

The Cook County Sheriff’s office has advocated since 2015 for Ms Hartman to receive treatment and stable housing in the community. They say she should not be in jail.

Ms Hartman, who suffers from mental illness, was arrested at Chicago’s O’Hare International Airport in October and charged with criminal trespass.

She was six months into a two-year probation sentence for successfully boarding a flight from Chicago to London.

It was her eighth such arrest. Under the terms of her probation she was forbidden from entering either O’Hare or Chicago’s Midway International Airport without a ticket.

She earned her nickname having been arrested for trying to board planes without tickets on several occasions.