I know what it's like to be skinny on top and have fat thighs. Tons of cardio and millions of low weight/high reps didn't help either. My thighs always looked fat, even when I was 17 yrs old and weighed 80 lbs (at 5'5")! So, starving and losing muscle is NOT the answer.
Finally I decided since my legs were big, then I'd make them big and muscular rather than big and fat. I started training legs hard and heavy. Squats, lunges, deadlifts, stiff-legged deadlifts - all the tough exercises women are told not to do, because it will make them "big"...
Moral of the story is my legs did NOT get big! They got hard, tight, and defined (nearly 2 pant sizes smaller). Sometimes I look at them and don't even recognize they're mine! For the first time in over 37 years, I actually like them!
I also do a lot of interval sprints for cardio. This has been good for glute development and quad definition. (I used to have a flat flabby ass too, but no more.) I changed my diet to include more protein and healthy fats. I had been eating too many bad sugary carbs, but not enough calories overall.