L.B.
Sorry to say, but the reason why she is "doing this" is because, unfortunately, you gave her the notion that her behavior is acceptable, and then doubly reinforced it by setting up a special bed just for her. She's learned to use the powers of manipulation to control those around her, which is also related to the other changes you've noticed - being clingy and perhaps a bit demanding, etc. Smart little people, those four-year olds!
It won't be pleasant, but it's absolutely necessary that you undo the damage, and as soon as possible! The real issue here is that your daughter must learn that it's unacceptable to manipulate others in order to get what she wants to please herself. Think of adults you know who possess this trait. Are they liked and respected? Are they happy?
Do away with her special bed in your room and tell her, matter-of-factly, that the "rule" in your house is that she must sleep in her own bed, in her own room all night long, and there are no other options available. Make sure you praise her at the same time, by telling her things like - you're proud of her for being such a big girl, and that you are confident she'll be good at following rules, etc.
If she gets up and comes into your room during the night, it's imperative that you return her to her bed, quietly and calmly reminding her of the rules. Conversation should be minimal, the tone of your voice void of emotion. If she fusses or cries, ignore it, refraining from any sypathetic replies, tell her you love her, good night, and leave the room. If she gets up again, just keep returning her to her bed, the less said, the better.
If you are consistent and stand your ground, she will accept the fact that you mean business, and she does not have the power to manipulate you.
You don't mention how many total hours of sleep your daughter gets, but at four years, I think 12 to 14 hours are recommended. Try to avoid food, snacks, or drinks, especially with any sugar content, a good hour and a half to two hours prior to bedtime. Digestion demands bodily activity. Try offering turkey and/or warm milk as a last snack. Both contain natural sleep-inducing ingredients.
Prior to bedtime, try to maintain a household environment that is calm and quiet, free of stimulating activity and noise. Play items should consist of things such as books, coloring, listening to soft music, etc.
Stick to your guns, be patient and consistent, and you will be rewarded with the trust and respect of your children.
Much good luck!