She was assigned to the TCS Tolmen part of the of the Honor Guard for the Diplomatic Corps that arrived to Firekka system. When the KIS Ras Nik'hra announced its defection to the Terran Confederation, several troopships were sent out, in case it was needed to board and capture the ship.
The Tolmen docked to the Fralthi-class, and Ralgha nar Hhallas opened the airlock for them. Marks emerged at the front of the human squadron and commanded the Kilrathi who were after their defector captain to not move. A Kilra'hra on the side of the airlock leaped at Marks only to be shot down by her. Then she repeated her command, noting that they'd be shot like prey animals otherwise. Being sorry for his former crewmen's lives, Ralgha told them they are outnumbered and unarmed and their deaths would be meaningless. Hearing this, they complied.
Ralgha welcomed "H'hristi Mar'hkss". She offered to bring their medical officer and treatment in their Sickbay, and then commanded the boarding operation. As the Kilrathi have problem telling Terran males from females, Kirha referred to her as "he" until someone corrected him.
She gave permission to Hunter to land on the Ras Nik'hra after he destroye the KIS Kraj'nishk. She waited for him with 2 marines, Ralgha, Kirha and Spirit and made the introductions. She instructed Hunter to accept Kirha's oath of fealty to avoid a diplomatic episode.
She commanded 150 Confederation Marines of Company Zebra to Firekka to assist the Firekkans against the Kilrathi. As they were transported to Firekka on the TCS General Powell, the Drayman-class was attacked and boarded and the marines put in the cargo hold.
The hijackers attempted to take the ship off-system, but the marines broke out and tried to retake the ship sustaining heavy casualties; 8 hours after the attack, Marks managed to send a message to the TCS Tiger's Claw. The Kilrathi realized that the marines retook the ship and took ships to destroy it. Prankster and Doomsday protected the transport against an external attack and escorted it back to the Claw. In the ship's Sickbay, she expressed her thanks to the pilots.
It's possible that Kristi Marks is a tribute to screenwriter and game designer Christy Marx.