What natural herbs can a woman use to regulate her periods?

I don't recommend. I'm skeptical any herbal product is a good choice. Some are harmless, many aren't. None are proven, tested, or regulated; the amounts and the ingredients can (and do) change often. Despite the popularity of so-called natural remedies, herbs, and supplements, you don't know what you are taking. If your period 'needs' regulating, finding the reason is easy and a better start than trial-and-error.