Poor you, sounds like a bit of a nightmare and interrupted nights are no doubt taking a toll on you too! Like you say children this age can find it difficult to explain their feelings or even know what the matter is themselves which makes getting to the bottom of the issue very tricky indeed! I have had similar problems in the past and after several nights of sympathy I have had to deliver some tough love! I think sometimes these things can become a habit and if they get cuddles and chats when they wake it can become quite a nice habit for them! Tough love did work for us, it's perhaps worth a try?
Another idea might be to buy a new cuddly toy and make a bit of a big deal of it being her new comfort friend for the nighttime?! Something she can cuddle when she wakes. Or I have used Worry Dolls (ttp://
www.amazon.co.uk/Tobar-Set-Trouble-Dolls...334867204&sr=8-2) with my son before - you tell them your worries before you go to bed, place them under your pillow and hope for a good night's sleep. Getting his secret worries off his chest seemed to help him a little?! You could secretly listen at the door to see what she tells the dolls?
But if there is something really really bothering her these suggestions might not work - good luck would love to hear how you get on as I'm sure lots of people have been/will be in the same situation at some point too.
Best of British!