I'd be fairly cautious about St Johns wort. I know little about it as a herbal medicine but I know in the natural herb state that it causes hyper-sensitivity to sun and increases the likelyhood and severity of sunburn. It's a noxious weed where I live because cattle that graze on it end up with badly burned noses and udders where they aren't protected by hair. I am sure you don't want your wife to end up with burnt udders...
Maybe in herbal medicine form they overcome that or the dose is low enough that its not a problem but I'd check it out pretty thoroughly before I put some in beer where the could be any risk of over-dose.