Talk to Pediatrician on Irritable Child

My niece is 5 years old. She is very intelligent but at a times she became so irritable that it's very difficult to handle her. Like she does not want to go back home from dada aba house or she sometimes does not want to go to school and this behavior got worse after birth of sister. Moreover, she does not eat properly. She feels her hands and feet are dirty all time so she wash it again and again. Is there any need to consult a pediatric psychiatrist or how to deal with this stubborn behavior. TIA