Try putting something in her bed that smells like you, or a stuffed animal or doll of yours if you have one. (My hubby bought me 3 stuffed bunnies one year for christmas and they usually sit on our bed - so when the kids have trouble sleeping, I give them one of my bunnies. In fact now they'll just wake me up and ask if they can have one and then go right back to sleep)
Also, I'd try making more and more trips out of the room to "get" or "do something". Fake a potty trip for a few minutes, tell her you need to go refill your glass if you're going to sit with her, tell her you need a pillow, or a blanket to sit on, or a hoodie because you're cold, etc...
Most kids will be ok with a quick trip (especially after they've seen you come back promptly once or twice). Gradually extend the number and frequency of your trips so she's used to you being out of the room more and more. Eventually she will remember that she doesn't need you anyway.
Excercise and fresh air are good ideas as well, although I read something that it shouldn't be TOO close to bed because it can actually keep you awake due to the active chemicals in your body..
Good luck!