In September 2015 during one of their meetings, a Muslim extremist entered and threw a jar of acid on the table, which left those at the meeting injured. Once at the ED, Denise was taken hostage by yet more extremists, who targeted her, knowing that she was linked with the far-right organisation. Preparing to execute her in the meeting room, they were only saved when the specialist police squadron located them and apprehended the terrorists. (CAS: "Belief")
In April 2017, Denise visited the ED to see Roy, who'd been involved in a fight outside a local pub. Her son Scott's behaviour grew out of hand, and Ethan asked him, Denise and Mickey to wait in the relatives' room. However, Roy later died and they found his body in resus before Ethan had a chance to tell them. Denise gave a damning statement to a TV journalist later that day, explaining that had the doctors not been on strike, Roy could have been saved. (CAS: "Reap the Whirlwind - Part Two")
In June, Denise was in the ED again when Mickey was admitted after a right-wing rally. She was quick to accuse a young Asian girl of assaulting him and when her mother arrived, Denise accidentally poured hot coffee on her. (CAS: "Swift Vengeance Waits")
The following month, Denise was back in the ED after Scott's fall from the balcony. Scott told her that Mickey was gay and she made him choose between them and his sexuality; he chose to be with Jez. Denise was heartbroken but relieved that Scott was on the road to recovery. However, he later took a turn for the worse and Ethan didn't help him. Denise found him lifeless in resus and he later died, leaving her distraught. (CAS: "Somewhere Between Silences - Part Two")Later in August, Denise targeted Jez, angered at his relationship with Mickey, and threw a Molotov cocktail through the front window of Robyn's house. However, Jez was upstairs at the time and instead Robyn and Charlotte became caught in the blaze. A short while later, Mickey arrived at the ED, to the shock that his mother may have been behind the attack. Jez asked Noel to call Denise, saying that Mickey was caught in the fire. She arrived at the ED a short while later, shocked at what she had heard on the phone. She later let a word slip, giving herself away as the perpetrator, to Mickey's shock. The next day, Jez caught Denise watching Robyn and Charlotte and chased after her. After having a stern talk with her, she realised she was in the wrong, but she was later apprehended and taken away. (CAS: Episode 1050)
Lucy Benjamin initially portrayed Denise Ellisson as a one-off guest character in 2015. However, she was later seen in the Spring 2017 trailer, confirming that she was reprising her role over 18 months later.