Answer: The genotype of the female fox is-
ww.
As per the given information in the question, white coat (W) is dominant over tan (w) coat in foxes.
Dominant trait (depicted by capital letter allele, such as W for white coat) masks the expression of recessive trait (depicted by small letter allele, such as w for tan coat).
This means that white coat is a dominant trait over the tan coat, which is a recessive trait.
The only possible genotype for tan coat is 'ww' (homozygous recessive), whereas white coat can be exhibited by two genotypes, WW (homozygous dominant) and Ww (heterozygous dominant).
As the female is tan coated fox, thus her genotype would be ww (homozygous recessive).