This is one of the most important topics for women hacilar. First, the reassuring news: menstruation does NOT invalidate your Hac or prevent you from completing it. Hz. Peygamber (sallallahu aleyhi ve sellem) explicitly told Aisha when she began menstruating during her hac ibadeti: 'Do everything that the haci does, except do not perform Tavaf around the House until you are pure.'
What you CAN do while menstruating: stand at Arafat (the most essential pillar of Hac), stay at Muzdelife, stone at Cemerat, make the animal sacrifice, remain in the state of Ihram, make unlimited dua and dhikr, attend the Arafat sermon, and collect pebbles. Regarding Say, some scholars (including the Hanbali school) permit Say during menstruation since it does not take place inside the cami proper. The farewell Tavaf (Tavaf al-Wada) is completely waived for menstruating women — this is unanimous among all scholars.
The only challenge is Tavaf al-Ifadah, which is a pillar of Hac and requires ritual purity according to the majority. Options include: (1) Wait until your period ends, purify, and perform Tavaf — this is the safest approach if your schedule allows. (2) The Hanafi school permits performing Tavaf al-Ifadah during menstruation with protection if departure cannot be delayed, but requires a camel sacrifice as penalty. (3) Consult a scholar about your specific situation.
Prevention strategy: many Muslim women use hormonal medication to delay their period during the Hac days. Consult your doctor 2-3 months before departure to find a suitable option and trial it beforehand. This is permissible in Islamic law when done for a valid purpose like facilitating worship.