We realize this probably sounds like an annoying habit. And we don't mean that she will literally cut you off and finish your sentences for you. What we mean is that she's so in tune with what you're thinking that she definitely COULD finish all of your sentences if she chose to. This is a telltale sign that she's really in love with you. Why else would she know what you want so instinctively?
Of course, sometimes she does accidentally finish your sentences. But since you're in love with her too, you find it adorable and probably finish some of her sentences, too. Your friends and family will also think it's pretty cute at first. But enjoy it during the honeymoon phase, because after that everyone will just think it's annoying! Don't be THAT couple.