Oh I do tell her in bed, I've done that a number of times, she doesn't care at all. She basically has this 'oh well, you can talk to me now!' attitude. She seems to be joking, but I don't think she realises how annoying it is. When we were in highschool nobody wanted to hang out with her and they'd always tell her to go away whenever she hung around (because she was afraid to be alone because people were so mean to her), and she would say no. No matter how cruel people were and no matter how many times people told her to go away she would say no. So I don't think she quite gets what 'leave me alone' means, no matter how nice or mean you put it.
So yes I've made it pretty clear when I'm not interested in talking, especially when I am literally lying in bed going to sleep in the middle of the night, but she still won't leave me alone.