| "You have no idea what you've just started."
— Spoilers for Deus Ex Universe: Children's Crusade follow!
On Adam Jensen's first official TF29 mission, the team is sent in to rescue kidnapped children and Niemi asks for clarification from Jim Miller, as TF29 does not normally handle such tasks. She and Zoe Beaufort are later assigned by Duncan MacReady to follow after him and Vasquez as they storm the warehouse, leaving Jensen behind at the evacuation point. However, they come under heavy fire and Jensen barges in, saving the team.
Later, when Jensen is cornered by the anti-aug reporter Titus King, she intercepts before Jensen falls for King's tactics and tells the reporter off, threatening him before slamming the warehouse door in his face and calling him an asshole. When Jensen asks her why Miller ordered him to not pursue one of the terrorists, she explains that Miller does not want the team getting caught on camera. She is then ordered by MacReady to sweep the warehouse for any hiding terrorists and finds a suspiciously locked security door, when the rest barely had knobs, and calls MacReady and Jensen over to investigate. As MacReady gets ready to blast it open with his weapon she objects, saying it could be booby trapped or he could hit anyone on the other side. While the team leader retorts that she watches too many movies, Jensen steps in and hacks the door, solving the problem and leading to Niemi rubbing it in MacReady's face. The three then enter the room to find 2 hostages handcuffed to beds, an augmented boy and a non-augmented woman. As they help the two out, MacReady asks what is the boy's problem as he is giving a sour look and Niemi asks what MacReady's deal is and that the boy is just scared, though the team leader comments the boy does not look scared. Another terrorist suddenly appears and Jensen chases after him, leaving Niemi and MacReady to help the hostages.
Niemi appears beside Jensen shortly after Beaufort helped him knock out the terrorist and they learn from the rescued woman that the terrorist is Bruno and he should be killed, but the boy retorts that he was helping them. MacReady then begins to question the woman on why she is there, who reveals she was forced to watch over the children or else the terrorists would kill her daughter, who is in Glasshütte, Dresden's aug ghetto. MacReady starts to grill her some more but Niemi tells him she is not the enemy so he turns his attention to Bruno, who has just woken up. MacReady threatens him and Bruno eventually draws the team's attention to Marek, the augmented boy that was isolated from the rest of the children. Bruno then reveals the woman, Helena, knows why but if she reveals anything, her daughter will be killed, leading to MacReady to punch him and tell the terrorist he will only talk to him, not Helena. Bruno ignores this and tells Marek that MacReady "should not take such drastic action, should he?" before repeating "drastic action" an obvious kill-phrase. Helena screams for them to run as Marek turns red and smoke comes from his eyes just before the warehouse explodes, killing Niemi.
- Based on the e-mail about getting together for drinks to remember Niemi, one can conclude that she died roughly 6 months before the start of Deus Ex: Mankind Divided.