If you have been checking your mail in Genshin Impact you will have received a letter from Diona. She went off in search of new ingredients to create a drink so foul that it can help her destroy the wine industry in Mondstadt. What she found were Loach Pearls, and she will send you 10 of them and a new recipe for a meal you can make.
In the letter, Diona mentions that she wants to come home, and asks you to come and find her. We have looked, and from what we can tell the rest of the Genshin community has also been looking, and so far nobody can track down where she is.
To find Loach Pearls, you need to be on the road between Stone Gate and Wangshu Inn, as Loach Pearls can be gotten from Golden Loach lizards that appear in this area. The area itself is called Dishua Marsh, and Diona mentions in her letter that she is heading along the road to try and find disgusting things to put in her drinks so that people will hate them. Unfortunately for her, all she can do is make wonderful tasting drinks that people love, making her the best bartender ever, but the worst person at destroying the wine industry. She is now tired and upset and wants to come home.
At the moment, we don’t know if this is all just some storyline, or if it will eventually lead to a quest, but we can say with confidence that Diona is nowhere to be found in this region at the moment. We will keep looking, and hopefully, something will come from it. For now, there doesn’t appear to be any way to actually find Diona out in the world of Genshin Impact.