×You need to wait until most of the guards leave. You also need to have a key to her cell with you beforehand. Lockpicks are not enough.

×You can wait in Aurvandel's room until the castle gates close, then sneak out. Snorri has the key.

×Wait in Aurvandel's room until late evening. Eventually he will walk away and escort you out. Go right back and wait an hour. Sneak back in. The guard will be patrolling between the hall and the prison. Sneak behind the statue on the left when he isn't looking. When his back is turned to you, throw a dagger to the vase to attract his attention, then sneak inside the prison. You want to hide behind the wall near the cell with Kraka. Open the lock and sneak out of the castle.

The key to the cell can be pickpocketed from Snorri in the tavern if you give him enough mead for him to pass out.