My sis won't eat.... and she's only 5! help please...?

my sis is only 5 years old and she won't eat anything!! she used to weigh 77 pounds...now she only weighs 50... how can me and my parenst get her to eat again? the reason why she isn't eating is in the same month in january my gma on my dad's side died...then a week later my mom's side gma died... and she's been sad about it.... i tried talking to her about it. but it never helps. how can me and my parents get her to eat again?