Probably a stupid question, but you have confirmed the beds are correctly assigned, right? I've noticed in my games sometimes the bed assignments reset.
If the bed she won't mess around in is definitely assigned to her, is it a different type of bed from the brother's?
I know this isnt my question, but im having the same problem. My sim and her parents (which is the bed my sim and her bf mess around in) are different beds. And i know for sure that the beds are assigned to her parents and i also assigned her bed to her and her bf.
@Sigmesophie If you use mods/CC, please test "vanilla". Drag the Mods folder to the desktop, delete the file called localthumbcache, open the game to test, and exit without saving.
