Lighting of the set mostly. Her sets in the dark/high lights only/dramatic lighting are most affected. Most digital cameras suck at taking low lighting photos and the photos have a lot of noise at low light. Sure,programs can reduce that noise, but the noise still there.
Her sets in full light/daylight are fine without issues.
Either that or you are noticing that her photographer likes using a 50mm prime lens. Which only has a small set distance of the photo in focus, leaving the rest of the photo out of focus. So if her face is in focus, everything else in the photo is out of focus a bit and more so the further away from the focus point.