Welcome to the forum.
Shooting sports, especially sports like football (large field), can really push the limits of your photography gear. This is why pro sports shooters use some of the most expensive gear; cameras and especially lenses.
For example, she'll probably want a longer lens. 200mm is long, but maybe not long enough, 300mm might be better. The problem is that her 18-200mm lens or any 300mm lens (zoom or not) that costs less than $1000+, will have a maximum aperture of F5.6. The trouble with that, is that it will be limiting in terms of how fast the shutter speed can be. And when shooting sports, shutter speed is fairly important.
That's why the pros use lenses like a 300mm F2.8 or 400mm F2.8. They are long AND they have a large maximum aperture...but that also makes them large and very expensive.
If she's shooting in bright daylight, the problem won't be as bad. The brighter light will allow for a faster shutter speed, but if she's trying to shoot at night, under the lights...then good luck. Even a pro's gear would struggle in that situation.
The good news is that modern cameras are pretty good at higher ISO levels. So she can turn the ISO up to 3200 (give or take) and that will help with faster shutter speeds.