"She's a fourth-circle who can use spellsilver from seven feet away, but if that was all we needed we could go grab a seventh-circle wizard for it or whatever. It's more that while the rest of you are doing whatever it is you do when I'm not looking, Carissa is spending a bunch of her time maintaining the critical Keltham component of the Project, and that whenever I have a task like 'so how do I actually get two hundred mice plus their living supplies if I need those' Carissa is the one who I turn to, she's the one who worked with me on figuring out requirements for the fortress you're now living in, etcetera."
"These salaries are based on the negotiating power you have, and the negotiating power you have is based on your irreplaceability. Carissa is the person other that myself whom it'd be most crippling for the Project to lose."