Diet, weight, cardio.
Diet diet diet.
Plus if she's dieting and starts to see some results in her upper body, she's still going to have to work it longer to see greater results in her hips. If she tends to hold the greatest concentration of fat cells in those areas (as most women do, due to estrogen), say a 4% drop in bodyfat won't be as apparent where there are more fat cells. But it is still working.
Also if she's been workign out for several years, if she's been doing the same thing this whole time, she might want to look at altering how she's working out -- does she do any cardio? IF yes, try HIIT. Traininig -- is she lifting heavy or lighter & higher reps? Then try heavier, lower reps. Super sets, etc.
And I can't repeat how much diet contributes to your ability to lose bodyfat. I lifted heavy for several years but until I tied in the diet, I didn't lose the bodyfat.