Hires fix or Tiled Diffusion (+ADtailer) would give good results.
(If interested in upscaling settings, see : https://civarchive.com/articles/3588)

Recommended weight: around 0.7-0.8
Triger Word: szn
Sample prompts: szn, 1girl, short petite, very long hair, parted bangs,
Alternative hair style: szn, 1girl, short petite, long hair, single braid, sidelocks, parted bangs,

V1.3: Overall learning parameters modified.