So, no "get regular" pill -- darn -- no fortune for us -- darn, darn, darn
Of course there is. It's the pill most women have taken at some point in their lives. The one that appeared on the market around 1960. Modern versions contain much less estrogen, of course. But either way, you take it for three weeks a month and then you don't take it for one week. (Maybe it's less than a week, but I don't really remember.)
Quitting for a week will prompt menstruation. So as long as the woman makes sure to stick to the schedule, she'll become regular. The pill is sometimes prescribed just to help women who're wildly irregular. Also to help women with acne and other stuff.