stumped for an answer then, best just to reassure her, put the lights on check there is nothing around. The only other thing I can tell you is that my dd used to say that there was a 'creature' in her room, I insisted that it was her imagination, she was 5 at the time, it turned out that we had a small field mouse and it had made its home at the back of her bed! I felt really guilty for not believing her, don't think this sounds the same in your case but I do think we should trust them when they tell us things. I got really cross with my dd and told her not to be stupid (bad mummy), there was a 'creature' all the time and I just didn't believe her . Lots of cuddles, reassurance, and treat her seriously whilst keeping an eye on anything that may be feeding her imagination. Good luck!