When you are elated, you are not just happy. You feel extremely happy and excited, almost lifted, because something good has happened or is about to happen. People use it after news that really matters: you got the place you wanted, your team won, a baby was born. It is a little more careful than “thrilled” or “over the moon,” so it sits well in writing and in polite speech, but it is not stiff or official. Though actually you would not usually say you were elated about a sandwich; the feeling is bigger than everyday pleasure. It describes the person (she was elated), not the thing that caused it.