Which allele combination is used to represent a female who has a heterozygous sex-linked trait

Let's look at the trait for colourblindness which is an X linked trait. Knowing that females have the sex chromosome compliments of XX. And the alleles for being colour blind is denoted as c, and the allele for normal vision is C.

The allelic combination used to represent a female who has a heterozygous sex linked trait, in this case colourblindness is X^C X^c. Only females can carry the allele for colourblindness and not be affected, she is a carrier for this disease.