She's a mage armor, basically a heavy armor that attacks like a mage. (so magic damage)
her AW ability gives 10 MR for ALL melee units, and her skill increases attack and def by a significant amount (60% at lvl 1) for the duration, although her current HP is halved when skill ends.
as for 'nothing else seems that great for a black' note that the primary thing that distinguishes blacks from the rest are instant skill on deployment. it's only by virtue of that that certain blacks end up seemingly more useful than others e.g. nanaly with her instant burst dmg and sybilla with her assassinate attack on deploy
so I'd say she's actually pretty good as a heavy armor that can tank both magic and physical. although granted her pdef is slightly low compared to black heavys like Deine even after AW.