My 9 yr old sis keeps havin breakdowns?

shes 9 and she will just start screamin and crying over nothing like i was babysittin her and she wanted macaroni and i already ordered pizza and she started freaking out then i was tryin to get her to do her hw and she started freaking out.. like over nothing she will just start crying and yelling and wont stop- my other sis is 7 and she gets like this to but not so bad! my dad and stepmom think they should like go to talk to someone or st idk but r mom left and it mite b becuz of that but idk they do it like all the time esecially when im babysitting idk wht to do? im babysitting my 9 yr old sister right now- and she is in her room but she wil probably do it agian.. idk what to do im tryin to be nice but idk what to tell them! my dad said to cal them if they do but that just makes her more upset its driving me insane- i think its cuz r mom left us and starting like a week ago doesnt talk anymore to us but idk how to help any suggestions! would be appriciated!