Are you sure you understood them correctly? Is it possible your daughter has premature atrial contractions and not atrial fibrillation? I am not a doctor but I have not heard of afib described that way and atrial contractions are not a danger where afib could be due to possible blood clots. Does your daughter have an unusually high heart rate keeping in mind children's heart rates tend to be more elevated than adults. An average heart rate for a baby in their first year can be anywhere between 100-160 from what I have read. Anyways, I agree with the previous poster. Contact the doctor's office to at least get clarification on your daughter's condition. Someone there should be able to at least answer a few questions for you from her chart. Take care and keep us posted on how she is doing.
Before waiting all holiday weekend so nervous, perhaps you can call the pediatrician office and there Will be a doc on call. Explain your concerns and I'm sure they will talk to you about that. In addition, if the doc dx. that, and then left on vaca, it seems the doc was confident that you could take care of your daughter at this point. If you see your daughter acting different in any way seek immediate attention, but perhaps once you talk with other moms that have similar situations you may be able to understand your daughters medical issue so much better. Thinking of you.