How to encourage my child to eat well? On good days she can eats like 2 full meals but on bad days, she refuses to eat anything.

Children are just like adult, some days adult don't feel like eating anything at all while some days has a very good appetite. I realize both of my kids experience this once in a while too. When he refuses to eat anything, just offer him some water and milk to comfort him. Sometimes, it might be due to overtired or feeling sick to eat. After a few days they will pick up the appetite again.