DD crying for nonexistent brother

Hi guys, so as the title says my 3 y/o daughter randomly cries out “brother” “where’s brother” “what happen to brother”. She’s an only child. I haven’t heard this on any show she watches..ntn besides she does have some small family figures but she never calls out for any of them, only brother. Like she could be doing literally ntn related to it and she’d just random cry those words out. It’s kinda freaking me out. Idk if I’m overthinking it or what. When I ask her what is she talking about she’s unable to explain.