I mainly did this for basketball but my youngest would pick a favorite player (TJ Haws) and would get a small treat every time they scored (like a sour patch kid). You could do something similar for first downs or turnovers or punts or TD's or whatever.

And most likely she will still get bored at age four. My second youngest often spent time sitting under my feet just playing on a phone but now at 14 is a very passionate fan.