If she has a favorite food that is nutritious, e.g., chicken fingers, Mac & cheese, give it to her daily. There’s protein, carbs, & fat in it. So the parent does not have an argument with her.

Make sure she takes a multivitamin a day and offer a balanced diet. You can also add pediasure 1-2 jars per day if there is poor weight gain. If she is gaining ok, just offer good choices and do not force feed. This promotes obesity later on.

Serve well rounded meals with no added sugar in any offering and let it be her problem, not yours

Many children in this age group are picky and fussy eaters.The most important thing is to first establish that the growth curve has not declined, that the child has not lost any weight and that the child is active and energetic.It is frequently the energy level and activity that distracts them from sitting still and having a regular meal.
Moreover, the child should have a CBC (complete blood count), to ascertain that there is no anemia, which can decrease the appetite on one hand and on the other, may be due to inadequate iron intake in the diet.
Children frequently also get bored with the same diet over and over again, so it is important to be creative and presenting the child with new foods, while maintaining a balanced diet.One common observation is that going to a restaurant, will most likely motivate the child to eat more because of the variety of foods.
I also usually advise parents, not to let the children play games on the ipad while eating, and not to play games in general, because it is distracting. Rather tell the child an interesting story during the meal.
Most of all, discuss this concern with your pediatrician, who knows the child best and can give you more individualized advise.