Answer: The sex of the child depends on the father’s sperm, not on the mother.
A woman has XX sex chromosomes, so all her ova carry an X chromosome. A man has XY chromosomes, so half his sperms carry X and half carry Y.
If a sperm with X fertilises the ovum, the child is XX (girl); if a sperm with Y fertilises it, the child is XY (boy). So the mother cannot be held responsible for the birth of a girl.