My wife took an emergency contraceptive(postinor2) after an unprotected sex and within 4hours we had sex again. should she take another?

Probably not, but...: Postinor2 or other emergency contraceptive pills work most of the time, but not all of the time. One should do a home urine pregnancy test 3 weeks after Postinor2, to confirm non-pregnancy. Also, use reliable forms of birth control so that emergency contraceptive pills will rarely be needed (hopefully never) in the future. A woman might use emergency contraceptive pills 0-3 times in a lifetime.