Herbs for Nudist to Delay Menstruation?

I'm going to a nudist camp in about one week, don't want to start my menstrual cycle while I am there, any suggestions? I got some Yarrow from our Herb Shop here where I live but the owner didn't know for sure if it works. I read that you have a list of herbs that prevent blood flow. Can you help me? No, I am not pregnant, my tubes are tied and have been for quite a few years now.

As a herbalist, my job is to help bring the body into balance. I can suggest herbs to help normalize the menstrual cycle, but not to delay menstruation.