I was always taught that it is long term high phe levels that doctors worry about most. Changes in phe levels are bound to occur when your daughter is sick, going through a growth spurt, has a change in activity level, etc. However, as long as they are not long term I wouldn't worry too much.
Growing up I had my share of high phe levels. Many were much higher than 4.8 (the recommendation for phe levels at my clinic is 2-6 mg/dl). Despite the high phe levels that I have experienced I am a college student studying nursing, a dancer on my colleges dance team, and a childcare teacher working close to full-time. I am happy, healthy, and fully functional.
I am sure if you asked the people with PKU here they would all agree that they have had high phe levels at some point in their lives, so I'm sure your little girl will be just fine.