So in Volume 13 of the light novel in Overlord, (spoilers)
it's clear that Neia gets stronger, however I'm not sure just how strong she becomes. For example, during the archery training, she manages to get perfect shots but indicates that she was not able to do so previously. Moreover, the first time she used the Heavy Recover spell, she was able to only use it once before running out of mana, but later she displays the ability to use it multiple times. If one were to compare her to the ranking system used by adventurers (copper, iron, bronze, etc., adamantite), where would she rank?
I'm a bit confused on how the leveling system works in the New World. Ainz mentions that he is unable to increase his levels and XP by killing off over 100,000 soldiers in the battle with the Re-Estize Kingdom, so how can Neia get stronger?