Isn't eroding the minds of rare boss-monsters way more efficient, then beating them? Her parallel wills rode on their mental link to mother, but it should also be possible with telepathy.
@AaniK: "What parallel wills?" Her other selves (the copies of her mind), that attacked mother
"What boss-monster?" Another big dragon, some other Demon Lord, angels, heros... Those kind of entities. If she can steal their skills by eroding their minds and sucking them dry, that's far better, than killing them the normal way and just gaining some experience points.
Sorry, somehow a comment about one of my favorite spiders ended up in a comment section of the wrong manga.