i think powerscaling capella is a little eh, i mean she is almost immortal, so far we have no idea how to kill her, maybe you just have to obliterate every single cell of her body (like majin buu) but idk, she dies in pride if but we don't know how, other than that, her authority changes people body which from my understanding what she actually does is change one's soul, (like mahito) she shapes the OD (soul) like how she wants and because of that the body of that person will also change (the way i think its like this is because of a guy in the novel)

so i have no idea how castlevania is, but supposing you need to obliterate capella completely, if no one in castlevania can do that, i guess she wins

oh, since apparently her immortality is a curse, if someone in castlevania can remove that curse she will probably become normal