I saw this scene while channel-flipping in the last 5 years, but the movie probably had a theatrical release. It was in English and in color, maybe released in 2000s or 2010s. I think this was the opening scene.
It took place in an empty European-looking city at night or pre-dawn. It had a vibe of not quite modern day, but also not super Victorian/pre-technology. There was a white woman in a billowing, long, satin-y, white dressing gown (or ballgown without all the petticoats) and she was running from something. She was barefoot, and there was maybe a shot of that coming down some stone steps.
It was a lot of her running through this city with no one else around, and you couldn’t see what she was running from. She was cornered somewhere (maybe next to a gate?) and turned to the camera. I think she had vampire fangs or a transforming-into-monster face in this shot. But she was definitely decapitated/killed by whoever was chasing her, and I think there was a shot of her head rolling on the ground.