Is a blood pressure of 98/79 normal for an 18 yr old female (5ft 7in, 115lbs)?

Blood pressures around 120/80 are normal for a young adult. There is a range and this would not be worrisome if the patient feels well, isn't having fainting or lightheadedness or palpitations. A persistent fast heartbeat could be a problem. If an abnormal blood pressure is found in a well checkup, it is usually not worrisome. Your doctor may suggest having a repeat BP measurement.

yes. it can be. if there are no symptoms of light-headedness, passing out, shortness of breath, discoloration, fast heart rate, chest pain, chest palpitations, then it is probably normal and not concerning