The Trapped Nixie - Act 5 Side Quest
Start Location: Wild Heathlands
Quest Location: Wild Heathlands
Objective: Escort Lili east to the water
Reward: 1 Skill Point + EXP
The Trapped Nixie Side Quest begins by speaking with Lili in the Wild Heathlands (pictured above). You can find this area by taking the Portal to Glauberg and traveling far northeast through a few zones. This Side Quest is one of two in Act 5 which will grant you a permanent reward for completing it, for this quest in particular you'll receive +1 Skill Point once it's completed.
All you need to do in order to complete this quest is speak with Lili in the central portion of the Wild Heathlands and run her to Suebi Lakelands to the east. Once you get close enough to the water in Suebi Lakelands the quest will automatically complete.
If at any point Lili takes too much damage she will return to her original location in the central portion of the Wild Heathlands. You will need to speak with her again to start the escort if this happens. I'd recommend either clearing the route from Lili to the lakes or after talking with Lili make a B-line straight for the lakes and ignore all enemies along the way.