Evelyn planned to take advantage of the 'dormancy' of the potent soul fragment, and slowly siphon off the soul power it contained until it was weak enough for her to wipe off in one go.
Of course, the entire process had to be carefully carried out in one go, and she couldn't just do it a little at a time. That would be far too risky, and could lead to the fragment being triggered accidentally at any point.
Disconnected from its 'owner', the piece of course had no ability to think or feel on its own, and remained unaware of Evelyn slowly siphoning more and more of its power as her own soul pool replenished, while the fragment grew weaker.
Most of the soul power was lost in the process of conversion, and Evelyn only obtained a tiny fraction of what the soul fragment actually contained. But this was also already equivalent to multiple level ups.
