Commander of the First Army
As of 3049 immediately prior to the Clan Invasion, Katherine Luarca had reached the rank of Precentor V, serving as commanding officer of First Army and overseeing all six Divisions within the Dieron Theatre.  Luarca remained in command of the First when Precentor Martial Anastasius Focht made its batchall with ilKhan Ulric Kerensky for the climatic battle on Tukayyid.  
Though outlining an overall battle strategy, as one of his more seasoned commanders Focht made the fateful decision to leave the running of the campaign's tactical side to Luarca as he chose to focus on assisting and directing his less experienced commanders. Overestimating the skill of her army and fearful that green Fourth Army would break under combat with the Clans, Precentor Luarca ordered them to stay and defend the secondary target of Luk as she sent the bulk of her First Army to harass the Bears, keeping only her veteran 103rd Division back to defend Spanac. While the Fourth's CO Precentor Aryon Tolliver disagreed with Luarca's decision, he chose to respect her superior experience and did not lodge a formal protest with the Precentor Martial.     
Unfortunately the First Army on its own lacked the strength to stop the combined might of the Ghost Bears's Alpha, Beta and Delta Galaxies. Though the 91st and 12th Divisions successfully blunted Beta and Delta's advance on Luk at the cost of the 121st Division, the Bear's elite Alpha Galaxy inflicted heavy losses on the 308th Division as it easily resisted the division's attempts to stop its advance towards Spanac, prompting Precentor Luarca to order the 91st fall back to assist in its defense.     
When the Ghost Bear Khans ordered Beta and Delta to join the advance on Spanac just as Alpha Galaxy and the 91st Division reached Spanac's suburbs, Precentor Luarca ordered the 12th and 308th to block them in the hope of buying time for the 91st to reach proper defensive positions. Save for 12th Division's brilliant ambush and destruction of Beta's 7th Bear Guards in Holth Forest, the bulk made it through relatively intact and the addition of Beta and Delta allowed the Bears to surge past the 91st Division, leaving only the intact 103rd Division to stop them.    
Recognizing her whole battle plan had been flawed but now left with no other options, Precentor Luarca ordered her seemingly doomed 103rd to defend the city no matter the cost. Katherine Luarca's desperate review of her over-matched defenses was interrupted by a confused Precentor Martial Focht who noticed the 91st's supply depot was about to be overrun and yet she had not reported her dire situation to either himself or his aide Klaus Hettig. When Precentor Luarca fanatically insisted with additional support from the surviving elements of the 308th she could hold, a utterly horrified Precentor Martial Focht fully reviewed the offensive and losses suffered in the Ghost Bear campaign and realised the guttered state of the First Army.   
Though Katherine attempted to defend her initial plan for the battle, the Precentor Martial angrily berated her for wasting her more seasoned force and likely dooming the defenses of both Spanac and Luk. Shocked and chastised, Luarca finally agreed to use the remains of the 91st to cover the withdrawal of the 103rd, Precentor Martial Focht viewing the loss of Spanac a lesser evil over the loss of a full veteran division. Apologizing for his outburst, Focht would plant the seed that saved Ghost Bear campaign when he suggested that Luarca strike the Ghost Bears supply lines when they advanced on Luk. 
Leaving Beta and Delta to defend their captured primary target, the Bears' Alpha Galaxy advanced towards Luk, the Fourth Army coming close to folding as Luarca had feared. Desperate to redeem her loss of Spanac, as the Precentor Martial had suggested, Luarca commanded the remains of the First Army in a strike against the Bears' primary supply depot at Spanac. Her attack forced the Ghost Bears to choose which was more important, the now vital ammunition or continuing the offensive against Luk. Eventually choosing to return to Spanac, while Alpha fought off the raid, they suffered such losses in the process that they could not resume the attack on Luk, with Clan Ghost Bear ultimately withdrawing with a draw.       
After the Ghost Bears withdraw, Luarca would continue to direct her troops after they were transferred to face other Clans such the Jade Falcons and Wolves. When an outnumbered Level II commanded by Adept Jeremiah Rose requested permission to pull back in the face of a Wolf advance, Luarca overruled him, ordering Rose to hold the line or die trying. 
Precentor of BattleMechs
Following the Battle of Tukayyid, in 3053 Luarca was promoted to the position of the Com Guards Precentor of BattleMechs, overseeing the procurement of hardware, supplies and parts and the recruitment and training of ComStar's BattleMech forces, with her former XO Katrina Troth taking over command of the First Army.  
- 20-Year Update, p. 70 "Com Guards (Deployment as of 3050) 1st V-iota"
- Tukayyid, p. 48, "Campaign: Clan Ghost Bear"
- Invading Clans, p. 29 "Tukayyid: World of Fate"
- Tukayyid, p. 53 "Spanac: City Under Siege  - Darkest Hour"
- ComStar , pp. 69-72 "History of ComStar - The Clan War - Battle of Tukayyid"
- Wolf Clan Sourcebook, pp. 48-49 "Tukayyid - Days of Armageddon - Ghost Bear"
- Tukayyid, pp. 55-56 "Luarca's Revenge  Unexpected Heroes"
- Main Event, p. 134 "Part 1 - Chapter 14"
- Field Manual: ComStar, p. 20, "First Army V-Kappa: The Bear Maulers"
- Field Manual: ComStar, p. 15"The Com Guards - Organization and Procedures - Command Structure and Operational Deployment"