All I can think of is that this somehow increases water retention, so a woman would be continually in the uncomfortable stage they quite naturally reach with PMS.
The formulation was supposedly orginally described as being for balancing female hormones.
Does the ad cite a paper in a reputable peer-reviewed journal explaining the methodology they used to obtain the published data? If not, assume it’s bull-puckey.
Wild yam is a source of “plant” estrogens. Estrogens can stimulate breast tissue. I would not advocate the product, though.
There is no regulation or standardization in the herbal industry today. I could go mow my grass, encapsulate the clippings, and call the result an all-natural herbal product.