Could my sister be going deaf?

Ok so she, always had a problem hearing ppl really since she was little... now since she's older she wears headphones to listen to music and stuff she keeps the volume extremely loud.... if i want to ask her something (Since she keeps her door locked) i have to pound on the door for her to answer and if her doors unlocked and you go into her room she won't even know your there even if you say something.... and recently she been having to ask ppl repeat what they said too her... i'm really worried about her does anyone know whats going on?