She's from Star Wars Resistance. Here's what the Star Wars Databank says about her:
A specially-trained member of the First Order Security Bureau with a mysterious scar on her jaw, Agent Tierny hopes to restore peace to the galaxy through absolute order. A master of manipulation, Tierny's tactics more often involve lulling her targets into a false sense of security rather than using more aggressive forms of interrogation. Her arrival at the Colossus platform, as part of a First Order security takeover, ushers in sheer chaos when the platform is plunged deep into the waters of Castilon, leaving only Doza Tower above sea level.
While Tierny was executed by Supreme Leader Kylo Ren because of her repeated failures to capture the Colossus, she still represented a more cold and calculating side to the First Order. Agent Tierny was a far more effective leader than her superiors because she favored calm manipulation over rage and fear. Her actions, in particular the way she convinced Tam to join the First Order, showed the subtle and overt manipulation that the First Order used to convince people to join their cause. Tierny's manipulation in Star Wars Resistance fleshed out the First Order more and made them even more horrifying because Tierny showed how good people, like Tam, could be convinced to do horrible things with the right misinformation campaign.
If you’ve seen the season finale of Star Wars: Resistance and know that Tam Ryvora (Suzie McGrath), a mechanic on the refueling station Colossus who has a good heart but suspicious nature, decided to side with The First Order. This wasn’t something she sought out. She was clearly manipulated by the First Order security officer Agent Tierney (Sumalee Montano), who revealed last episode that she had good reason to doubt her fellow mechanic Kaz Xiono (Christopher Sean) — he’s a Resistance spy. When you don’t trust someone, it’s hard for them to trust you back. So, Tam takes this news hard. Now that she knows her friend has been lying to her, Agent Tierney has her hooked. In the end, a confused and isolated Tam takes her hand and joins up with the bad guys.
Wookieepedia says this, in the first paragraph about her, in her entry on the fandom site:
Tierny was a human female who served as an agent in the First Order Security Bureau during the conflict between the First Order and the Resistance. In 34 ABY, she was sent to the supertanker fuel depot Colossus on the planet Castilon to root out the Resistance presence on the station. While there, she interrogated the mechanic Tamara Ryvora, whose colleagues Kazuda Xiono and Jarek Yeager worked for the Resistance. After presenting herself as caring and sympathetic, Tierny manipulated Ryvora into joining the First Order as a pilot and betraying Xiono and Yeager, making the mechanic believe they never cared about her. Tierny, Commander Pyre, and Ryvora fled the Colossus before its jump to hyperspace, boarding the Resurgent-class Star Destroyer Thunderer, where Ryvora was accepted as a First Order cadet. Over the following months, Tierny and Pyre pursued the Colossus across the galaxy. Using Ryvora's comlink, they tracked the station to the planet D'Qar but were unable to prevent the platform from escaping. Tierny devised a plot to have an engineer—Nenavakasa Nalor—sabotage the Colossus, but it proved unsuccessful
Also, she has a Villains Wiki page, calling her an oppressive manipulator, and saying she committed crimes such as corruption, sedition, murder, espionage, oppression, genocide, aiding and abetting, mass destruction, and death threats.