You don't think she could have been hungry at all? It is possible that she is beginning to teethe - some babies start quite early, but it is really hard to know. Often there isn't a lot to look out for, sometimes you don't see anything in their mouth at all because a lot of the pain is caused by the movement of the teeth inside the gum, before it is even close to the skin. If she is like that again tonight, I would try feeding her first and see if that helps just to rule out hunger as a cause.