I believe this is a foreign film. It has an older girl that always wears an armband. Her brother dies in the film and we see that the family has a culture where they keep the body at home before burying it. She either runs away or is on the run from someone. We also see later that she always wears the armband because she self-harms beneath it.
This sounds like the Japanese funeral tradition. They keep their dead relatives close for some time. Clothes at the funeral are always white.
Can you confirm it to be a Japanese film, did it contain Asian or Japanese people? If so you’re then you’re a step closer to your answer.