An extra on the latest Transformers film who suffered significant brain damage when a stunt went badly wrong has been rewarded $18.5m in compensation by a Chicago judge as part of a settlement.

Gabriella Cedillo, then 24, was one of 80 extras brought in to appear in the background of an action sequence shooting in the city of Hammond, near Chicago, on 1 September 2010 for Transformers: Dark of the Moon, the third film in Michael Bay's series. At the time of the accident, she was driving her own car, a 2006 Toyota.

In their suit, Cedillo's lawyers claimed the aspiring actor was hit by a snapped cable which had been pulling another vehicle involved in the stunt. It crashed through her windscreen and struck her in the head. Neither Paramount Pictures nor DreamWorks Studios, the film's production partners, had a permit for fireworks or explosive devices on the day, and lawyers argued that a "completely inadequate superficial weld had been applied in a failed effort to secure the bracket to the [stunt] car", according to NBC Chicago. It has also been revealed that the same stunt had failed the previous day, resulting in its abandonment.

"I think they were well aware of what was going on out there," said Cedillo's lawyer, Todd Smith. "They were actually announcing on the radio, that, watch out for the debris. The people were driving around, apparently, trying to dodge debris as they drove along."

He added: "She will be taken care of. I wouldn't have resolved this case if I didn't think so."

After the accident, Cedillo was airlifted to a nearby hospital where she underwent emergency brain surgery. She had lost "about a third of the top of her head," according to her lawyer. The injured woman's legal team launched multiple lawsuits against the two studios, but allege both organisations did everything they could to avoid a payout, though they did initially offer to cover the victim's medical bills. These totalled $350,000 alone in 2010 but no payment was received, resulting in Cedillo being forced to cover her bills through the US public aid system. Transformers: Dark of the Moon went on to take more than $1bn at the global box office.

Cedillo is now undergoing therapy at the Rehabilitation Institute of Chicago and reportedly remembers nothing of the incident. "We're hoping for the best, for her to continue her education, maybe some day get married and so on. But, you know, we'll just have to wait and see," her brother, Rudy Romo, told NBC.

The film industry blog Deadline reported on Wednesday that the settlement would have been delayed even further had Cedillo's lawyers not attempted to pull Transformers' high-profile director Michael Bay and his Platinum Dunes company into the suit. A Paramount spokesman told Deadline: "We are pleased that the Cedillo family has agreed to move forward with the settlement. This was a tragic accident and our thoughts and prayers remain with Gabriella."