What were her symptoms? You just say she had an allergic reaction, but you don't specify what happened. Was it hives? Was it gastric in nature? Did she suddenly have trouble breathing?
Nothing pathogenic can grow in beer, BUT people can have allergies to beer ingredients, someone could have an allergy to hops, or yeast, or the gluten in the grain, someone could be lactose in tolerant and have gastric issues from a sweet stout.
There's going to be two kinds of reactions, things like hives and respiratory, like a peanut allergy, and someone can get cramps and the runs-which is more like a lactose issue.
But they are going to be pretty immediate, the hives and resp are going to happen within minutes, if not sooner, and the GI would still more than likely happen within an hour maybe 2, but 20 hours, doubtful.
And the thing is, if someone is allergic to most of the beer ingredients then a) then they will be allergic to all beers, even commercial, unless it is yeast, then it would be with SOME commercial beers, that are unfiltered. BUT they would also then be allergic to bread as well. Since the same yeast is used in baking.
The hardest one to figure would be a hop allergy, since except for beer, hops don't really appear in other things. BUT then also, the person would be allergic to other beers as well.
SO I'm going to say it's doubtful that she has an allergy to your beer.