The cross of Li (father with skin condition) and Mai (mother with normal skin) will result in the following offspring:
Gemma - first child with skin condition
Sister of Mai - with skin condition
Parents of Mai - normal skin
Brother of Li - normal skin
Sister of Li - with skin condition
Mother of Li - with skin condition
Father of Li - normal skin
The father of Li has normal hair crossed to mother of Li with skin condition. The result is 100% heterozygous/ 50% probability of normal skin and 50% probability of with skin condition.
Li is heterozygous (Ss) and Mai is also heterozygous (Ss) since one of her parents might be carrying the recessive allele because of the offspring with skin condition.
The result of the cross is 25% homozygous for with skin condition, Ss 50% heterozygous, and 25% for normal skin.