Mandeep joined the CSN during Operation Menelaus with Grendel's Mother, though the operation was ultimately a failure.

Sima Mandeep was in attendance at the IWC general assembly at Alba when the news came in that Ifrit had been shot down over Mythos. She joined both Elliott Parks and Amanda Jenkins during the preparations for the rescue effort, volunteering to bring Grendel's Mother to the Coyote system to assist.

Mandeep did not arrive at Mythos until late into the battle around the planet, having had her position of authority largely stripped. Though she was acting captain of Grendel's Mother, her decisions were ultimately at the mercy of the goals of Adrian Parsons who had assumed full command over the ship and the operation.

Mandeep attempted to override Parsons' command aboard Grendel's Mother when the man ordered that Parks be arrested and held back from any direct involvement in the battle and his desires to effect Operation Sudarberg within the next few hours. Parsons' threatened her with a stay in the brig and a court-martial immediately after, should not back down. When Parks was taken from the bridge, she was on her second strike, with Parsons reminding her with a show of three fingers that she was close to the fate he was promising should she cross him again.

Mandeep came searching for Parks when the evacuation order was sounded on the ship, following its boarding. She found him incapacitated and almost unconscious after his fight with Anthony Hawke, who was about to finish him off. She subsequently attacked Hawke with a fire axe she was brandishing as a weapon, beheading him after a short struggle. She then helped Parks off the ship, leading them both to the escape pods.

She felt sorrow at Grendel's Mother's destruction, as she had served aboard the ship for a number of years and had hoped to see it survive its service until it was naturally decommissioned.

After the destruction of Grendel's Mother, Mandeep took over command of Amarok, another of the UNF's starfighter carriers. She took the carrier to the Adetton system, as part of phase two of Black Widow. The carrier was heavily damaged during the battle, the bridge itself (though deep within the carrier) being hit by enemy fire. Mandeep escaped uninjured.

Mandeep married Parks in a small ceremony in Gabriel, in November 2622, before Parks split the allied forces down the middle and took half to meet the Pandoran fleet. Mandeep kept in touch with him via electronic messages, but did not see Parks for nearly three years after they were married. Both Parks and Mandeep agreed that they wanted a family together, but that they were probably too old to have children of their own. They chose to adopt and also planned to buy a house near to a beach together, once the war was over.

Mandeep helped to fight the Pandoran fleet at Alpha Centauri, before retreating to Sol and assisting with the strategy meeting there. When it became clear to her that Parks was intending to make his way to the HD 21563010 system, she begged him not to go. Parks refused to promise her that he would return and so she let him go, asking him to be careful. Chaz Koonan later returned her wedding ring upon Parks' death aboard the Elpis' Gift.

Mandeep took part in the final battle for the Solar System, commanding Amarok and using the carrier's offensive measures to take down two frigates, as well as crippling both the Silversmith's Repoussé and Alysha's Calling.

Following the conclusion of the war, Mandeep adopted a boy and a girl and made an annual Christmas trip to Elliott's Rest, the system formerly known as HD 21563010, where she spent the day in honour of her late husband.