I have found the answer some machines require --gpus "0," see the corrected script below:

python main.py --base configs/stable-diffusion/v1-finetune_unfrozen.yaml -t --actual_resume model.ckpt --reg_data_root outputs\txt2img-samples\samples\woman_ddim -n rhaenyra --gpus "0," --data_root training_samples\rhaenyra --batch_size 2020 --class_word woman