I say, and with God's success: Menstruation prevents Tawaf; because it is performed in the mosque. If she performs Tawaf, she has sinned, but it is valid, and she is released from her Ihram by performing the Tawaf of visitation; however, she must sacrifice a camel as atonement for it. Refer to: 'Umdat al-Ri'ayah 1: 130, Sharh al-Wiqayah p. 125, and Manhal al-Waridin p. 146, and God knows best.