I feel that you kid is having an allergic component which is landing her up in frequent coughs and colds. If it is always associated with fever, it could be an episodic viral wheeze or if not a multi triggered wheeze. Both of these may gradually diminish over time. Coming to the diet part, as such any diet which is palatable for the kid can be given. If she is not eating what you want, try giving what she wants. At her age interest in play increases and interest in food decreases. This is quite natural. If she is active and playing around you need not worry. This age rather than the quantity of the food I suggest you concentrate more on the number of times you feed her and also make whatever you feed him calorie dense by adding good amount of ghee to it.
Regards - Dr. Sumanth