This was updated in the 1.5 rules update to have the defense tag. This adds some value, eg. letting you pay for it with Nerves of Steel or picking it up with Jocasta.
SHIELDMAIDEN (#11) Should have the Defense trait and read: “Hero Interrupt (defense): When the enemy with Death-Glow attached attacks, declare Valkyrie the defender without exhausting her. She gets +2 DEF for this attack.” (Added “(defense)”.)