This page of the guide to Resident Evil Village , provides a description of the boss fight with Lady Dimitrescu's first daughter in the castle basement. The following tutorial will tell you what to do when you encounter the vampire and how to defeat the boss.
The fight with the vampire takes place when you're exploring the basement of Dimitrescu's castle. After she appears, don't try to attack her right away, as she will turn into a cloud of flies and take no damage. Instead, going through the basement in a linear manner - you have to turn right or left at appropriate moments to avoid blocked pathways. Eventually, you will reach the stairs located behind the place where the vampire appeared.
As you escape, it's a good idea to look around for supplies, which will include ammunition for your pistol and shotgun, as well as ingredients for crafting more ammunition. Ethan needs to reach the boarded barricade and after interacting with it, he will start pulling the boards out. There will be a scene where the vampire catches Ethan, but this is scripted and you don't have to worry about it.
A shutter will be broken in the room, which is an important hint on how to win the fight - Lady Dimitrescu's daughters are sensitive to the cold. This means that you should attack your opponent when she gets near the destroyed shutter - this is where the icy air enters the castle room. She will then be exposed to gunfire - it is best to use a shotgun at first. Only after you run out of shotgun ammo should you switch to a pistol.
Stay near the shutter, wait for the vampire to appear, and keep attacking her. The fight shouldn't be very long. After receiving enough damage, the vampire will turn to stone and then fall apart.
For defeating the first vampire daughter, you will receive the Treasure - Crystal Torso. It's worth selling to the merchant Duke as soon as you have the chance.