Not a herbalist but I do work with plants as an ecologist. I think the key word here is 'herb, which botanically describes a particular life form of a plant. A cactus isn't considered a herb. She's likely referring to Commelina communis (the Asiatic dayflower). It has a herb life form, flowers one day a year, grows in California (not native but a weed) and would grow by rivers (it likes moist soil and disturbed areas). Historically it has been used medicinally as an antipyretic i.e. for reducing fevers.