According to the wiki, it was originally a typo, but a couple of months after release they buffed her to actually be a 12t Barrier...
But since it doesn't stack, it's quite meaningless. It's better than 3/5 turn Barrier sure, but honestly, the buff isn't that much of a deal. The Vigor buff and Thunder healer are what make Thunder Aphrodite, and particularly the synergy between all three of her skills.