Did this customer usurp the rightful due and effort of the tailor after backing out of the agreement, then pushing her to finish the dress in record time while pregnant, and then refusing to pay the full wage under the pretext of errors in the dress, even though she had initially affirmed its quality?

If the woman asking the question can correct the mistakes in her work, she should do so, and she will receive the full payment. If she cannot, then the owner of the garment has the right to reduce the payment by the value of the defect, as estimated by experts, and not by her own judgment. Withholding the full payment is an injustice and a disregard for rights. A minor error that does not spoil the garment may not warrant a reduction in payment.