It's a side quest in Alfheim. Once you enter inside and take something, not necessarily the main item you need, you can't escape until you beat the boss.
And guess what? I just kicked her ass into oblivion.
It occurred to me right before starting a new main quest to simply try with the Stone Wall shield, aka "
easy mode shield", upgraded it to the max available at this point and the battle became a walk in the park.
Totally relatable, hated that section. But keep playing, won't take long for the game to redeem itself.