Maybe pretend you don't know but gently lead her into another one of those mother-daughter talks we all love so well. In this one, mention the early symptoms, how to discreetly mark a calendar so she can be "prepared" a day or two before she starts at night, how to wrap and dispose of pads so that the odor doesn't give offense. In other words, the practical aspects of being on her period, including why she can't swim in a pad. (Maybe a demonstration in the sink with kool-aid to show her how it will lead?)
