She hadn't been a Spirit originally. She was the consciousness of the Orithyia Galaxy's life support contingency—the Star of Lightning.
Eventually, she managed to sever her link to the SOL and took over the body of a dying Spirit. By absorbing that Spirit's soul, she gained 'Spirit Race Factors'.
This was how Kaylatheurge became a Spirit.
But in the end, she wasn't a 'pure' Spirit, so while she inherited some of the race's advantages, she didn't inherit all the drawbacks—one of which was their below-average-growth rate.
The body she took over originally belonged to a Senior Spirit Lord, and all that power transferred to Kaylatheurge, who then built on that strong foundation and advanced it to her current level as a Spirit Empress.
She had grown powerful enough that Spirit Contracts became completely unnecessary. Whatever benefits those contracts offered, she didn't need them.
That's why she'd been so certain she'd never have to form one with anyone, under any circumstances.
