Of the first 60,000 customers who sent a true response to the incentive mailing sent by the marketing department, how many of them are female?
RESPONSE = 'true'; SEX = 'Female';
SELECT COUNT(T1.ID) FROM Customers AS T1 INNER JOIN Mailings1_2 AS T2 ON T1.ID = T2.REFID WHERE T1.SEX = 'Female' AND T2.RESPONSE = 'true'