As far as I can tell, Greg just strongly implied that she lost her arm as punishment. From “Time Trap” Chapter 2 (https://wallofhistory.com/read/?id=437):
Lariska laughed sharply. “You know better than that.” She jumped from a standing start into the rafters, executed a series of complicated gymnastic tricks, and then did a perfect dismount to land in front of her leader. The Shadowed One could not help but be a little amazed at her fluid skill, considering that her left arm was completely mechanical.
“Reporting,” she said, making no effort to hide her sarcasm.
“In the vault.”
“ All of it?” the Shadowed One asked pointedly.
Lariska glanced at her mechanical arm, then back at the ruler of the Dark Hunters. “ All of it. I remember my lessons well, Shadowed One, especially the painful ones.”
The Shadowed One smiled. “I find it hard to believe even you could eliminate an experienced Toa so quickly. Tell me the tale.”
To me the glances made clearly imply that her mechanical arm is the result of a “painful lesson”, probably from TSO.