"I've completed all quests received except the one you can't complete yet." -> What event can you not complete?
You're probably either missing the events with Kayelinth's mother, which start at the jewelry store in Thremten, or your relationship with her is not high enough.
The walktrhough has a step-by-step guide for the events of the main characters. You should be somewehre around these steps:
3. The next step requires 70+ relationship and you need to construct the bathhouse on the country overview map. (Oral CG)
4. You can now find Kayelinth's mother Jaylin in the Jewelry store in Thremten. After helping her in the search of her daughter, she'll move into the castle.
5. The next event requires that you're entered Minsk Harbour during the main story, that Mira had the event about her wings (second sex scene), and that your relationship with Kayelinth is at 100+. It starts with a dialog in the sleeping chamber, where Kayelinth will ask you to go to the Greencoast Tower. (First flight CGs)
6. Talk with Kayelinth to get the “Food Town” quest. Afterwards you can talk with her again in the castle for the next step of these events. (Tail masturbation scene)