Class is being used to describe what the character does. In this case, from the majority of fantasy settings and historical things I know about, "paladin" was used to describe a holy knight, and sounds better than just saying "holy knight".
In terms of my setting a paladin is a religiously-motivated knight who uses holy symbols and often enchantments on their weaponry tied to their deity, in Tanya's case the divine fires of Reon granted to Repharion.
As this is not D&D I assumed people would take paladin to simply mean "religiously-motivated knight" as it does in many non-D&D settings and not begin arguing over the definition of it.
Paladin meaning "tank with white magics" isn't a strictly D&D thing; it's present in virtually every RPG that includes the class. Even in games that don't have strict class systems, "Paladin Builds" pretty much always mean having white magic on the side. If you lack them, you're a "Knight Build", since knights are expected to obey a code of chivalry in the first place. In Dragon's Dogma, for example, you'd go Mystic Knight, and pick the Holy Wall, Holy Glare, and Holycounter techniques. Dark Souls is more flexible in weapon choice and also more melee-oriented in the first place, but has a number of useful Miracles that any decent paladin build wouldn't neglect.
In hard RPG terms, Tanya's a fighter with a lawful good alignment.
Enchantments, as a thing that affects specifically weapons and not people, wouldn't be typically limited to a singular class unless that particular enchantment made a note thereof, and even then, if the enchantment is caused by a divine blessing they typically only restrict the weapon to certain alignments, if that. And Repharion isn't even noted to have those restrictions.
Knights are expected to follow a code of honor and often be pretty religious on top, so you could have just listed her occupation as "Knight" and it would make sense. Maybe Templar or Crusader, if you want that religious fervor flavor.
