A., give her a sticker (We used a smiley sticker) every night she stays in her bed.. we printed off a calendar
http://www.dltk-cards.com/calendar/ and it has one of her favorite characters on it, princeses, Hello Kitty, animals.. anyway, I got the smilely stickers and explained that I was a tired mommy and since I didnt' get my sleep I was a crabby mommy who was NO fun! The smiley sticker represented that Mommmy and Daddy were happy that we got our sleep and so did she.
After 5 of 7 stickers the first few weeks, she earned $2 to go to the Dollar store to get something SHE wanted or traded them in for Disney Dollars at the Disney Store
We did this 5 out of 7 days the first few then we up'ed it to 6 of 7 days ... we explained to her what the 'scoop' was and praised her for every night she stayed in her bed. (We coslept too till she was 3 1/2, she is now 5... we had to implement this system in May and June this year.
Anway, by week 3 she was in her room all the time.
I also gave her a T-shirt as she said, it smelled like me although it was clean...??? but this is what she uses and more so I work overnight on weekends and she stays in her bed.
Try the reward and praise for the time she stays in her room... and follow through with the calendar and stickers first thing in the morning. My DD always looked forward to it.
I too would get some books about dreams/nightmares etc... on a child's level from your local library and read them together.
One thing we also do in our family is to pray, and I remind her that our faith believes we never have to be afraid as God is ALWAYS with her.
Good Luck and remember to do what is best for you and your family.