Asia is correct. No one should say that they love the person at the beginning of the relationship (unless they're referring to the friendly kind of love). I can understand strongly liking someone, I mean, why would you enter a relationship if you didn't like the person. lol.
Sorry if that sounds mean in any way. I'm just not one of those people that believes in 'love at first sight' or saying you love someone three days into the relationship. My mate and I probably started saying it after a month (which to most is probably early), but that is enough time (in my mind) for you to know that you love someone (plus, I had been friends with him for two and half years before we started dating). And by how you are talking, it sounds like she asked you fairly recently, so yeah.