But Trelawney got in.
Trelawney wasn't trying to disturb Malfoy.
Malfoy asked for a room where he wouldn’t be disturbed.
But Trelawney got in.
Actually Malfoy asked for a room to hide something in and so did Trelawney. That’s how she got in. Harry also asked to have a room to hide something in(his potions book). I think he was given the exact same room and didn’t realize it.I’m basing this on the description of the items in the room.
But Trelawney got in.
Malfoy asked for a room where he could hide something. When Harry is hiding his potions book from Snape he puts it in the room of requirement and sees the vanishing cabinet. Trelawney is looking to hide her empty sherry bottles. Apparently, the room responds in a similar way to similar requests.