I found the character difficult to replicate just by adjusting the prompts. After several minor modifications using img2img, the resolution was increased using SD upscale.
Prompt
(Masterpiece, best quality :0.99), (letty whiterock:1.15), outline, (1girl), solo, light smile, happy, highly detailed symmetric faces, (pupil:1.1), (gochuumon wa usagi desu ka?:0.92), (hitoribocchi no marumaru seikatsu :0.92), (shiny hair:1.05), (shiny skin:0.95), beautiful detailed girl, (loli:1.08), (child:0.975), (loli face and big boobs:1.15), (chubby:0.8), (thick thighs:0.87), (huge breasts:1.02), (large breasts:0.98), medium hair, [white hair:light purple hair:0.8], (wavy hair:1.1), purple eyes, (white headwear, (blue vest:1.05), puffy long sleeves, purple skirt, skirt set, (waist apron:1.05), (purple tabard:1.1), white footwear, boots :1.07), (white scarf:1.1), outdoors, snow, snowing, snowflakes, Snow Forest with Trees
Letty whiterock
I found the character difficult to replicate just by adjusting the prompts.
After several minor modifications using img2img, the resolution was increased using SD upscale.