Valerium
I haven't looked this up yet, but did Anne have some sort of health problem(s) that are known?
In the beach scene, her mom asked her to get out of the water b/c she knows how frail she is, and then, after she has the nightmare about Hannah, her mom tells her to take her valerium b/c it'll maker her feel better. (According to Wikipedia, valerian, which I'm assuming is related, can be used for anti-anxiety purposes and/or sedation, among other things. Maybe that was a common herbal aid in those days...?)