I am worried and need some help in the form of comforting words - that she is not pregnant - and advice from you.
Sorry, no comforting words here. The fact is, pregnancy is a possibility. There is no form of birth control that's 100%, including the morning after pill. The only form of birth control that is 100% is for her to keep her knees crossed, and you keep your pants zipped.
You'll have to wait and see. It's way too early to test, and the morning after pill can throw off her period. So wait at least a month, and if she doesn't get a period, test using first morning urine. Those are your options.
If you get lucky and she's not pregnant, then learn from this. Sex causes pregnancy. If you're going to have sex, even with protection, you have to be prepared for parenthood, because it does happen, more often then you may realize.