You two are talking past each other. You're treating "evil" like a type or class to which things can be members regardless of their behavior.
@Steampunkette is saying that your morality is exclusively and exhaustively determined by your actions.
You are speaking in terms of practicality/utility/definitionally and she is talking about things in absolute metaphysical terms.
You think that good/evil is something that you
are, but she thinks evil is something that you
do.
"Alignment realism" is, in my opinion, untenable for exactly the reason you two are struggling to come to terms. You can be a moral realist without giving alignment some sort of real metaphysical weight. You can be forgiven though, since D&D has for a very long time enabled that assumption with spells like "detect good/evil". So your interpretation might be more supported by the rules and lore of D&D... but that does not make it the more rational of the perspectives.