Is this the reason why my cousin acts the way she does?

She is 3 and a half years old. She cries a lot and always wants to visit me and she always whine sand tries to get my attention. She does this by hitting my younger children(ages 2 and 3)and when I yell at her for it she cries. I suspect she does this because her mother never gives her attention and mistreats her, I remember her mother visiting me and the child was scared of my cat and she cried and screamed trying to get away from it and then her mother yelled at her. She also gets very tense around her mother. Is it because she shows her little to no attention or is it something else?