from diffusers import AutoPipelineForText2Image
import torch

device = "cuda" if torch.cuda.is_available() else "cpu"

pipeline = AutoPipelineForText2Image.from_pretrained('black-forest-labs/FLUX.1-dev', torch_dtype=torch.bfloat16).to(device)
pipeline.load_lora_weights('Keltezaa/willow-rosenberg-flux-buffy-the-vampire-slayer-series', weight_name='Willow_Rosenberg_Flux.safetensors')
image = pipeline(' this is an image of a young women with shoulder length red hair, red and black corset, gothic short-sleeved, standing in an alley at night, full moon, wicked grin, hungry eyes, otherworldly look, vampire, fangs').images[0]

For more details, including weighting, merging and fusing LoRAs, check the documentation on loading LoRAs in diffusers