Does triggered mean a shadow card is revealed or does it mean the shadow card resolves? What I’m asking is can you keep the shield’s +2 DEF benefit but still cancel the shadow effect through Hasty Stroke, Sterner than Steel, Balin, Erkenbrand or some other method?

Looks like the answer is yes. The language of all those shadow cancellation cards talks about the shadow triggering as what allows the cancellation to happen. This makes Round Shield quite useful given its cost, especially early on where other options might not have yet presented themselves. I’m guessing that a third to a half of shadows are the ones that raise the enemy’s attack, so Round Shield works as a repeatable cancel against them. And for the other shadows, a boost to DEF can’t hurt.

I’m really liking this card.

I have a major beef with this card. There is space for flavor text, and yet there is none. Have your read The Battle of the Pelennor Fields chapter recently? From the moment Dernhelm reveals herself:

"But the helm of her secrecy had fallen from her, and her bright hair, released from its bonds, gleamed with pale gold upon her shoulders. Her eyes grey as the sea were hard and fell, and yet tears were on her cheek. A sword was in her hand, and she raised her shield against the horror of her enemy's eyes."

I imagine this must have been in the art brief. I know there wouldn't be room for the whole quote, but a missed opportunity for including either the first or last sentence.

But it's a great card, I like it particularly on allies. Or, especially thematically, Éowyn with a Golden-Round Shield