I feel for you. After our third childs birth in October, my five year old stopped sleeping altogether at night, she was basically living off of three to four hours a night, it lasted five months but we seem to be back on track. It was so bad that she wouldn't sleep unless we were staring at her. Basically the advice we got, which helped, was try not to make a big deal out of it during the day. Have her sleep on some blankets on your FLOOR, try ASAP to get her out of your bed. My daughter spent about three months on our floor right next to my side of the bed, eventually she moved to the end of our bed on her own, etc. Did you daughter have any big upheavals this year, starting kindergarten, birth, death, divorce, a move etc? Evidently those all spark sleep issues. We tried everything from punishment (I know that wasn't the right way to go about it, but you lose it after awhile) to rewarding for sleeping. A friend of mine suggested a reward system using beans. If she went to bed on her own without mom or dad in the room she would get three beans and if she slept through the night another five and when she reached a certain number we would do something fun like a playdate, park, chuck e cheese, whatever.
It took a long time, but things seem back to normal, she also needed some alone time with me during the day, I KNOW it's so hard with four kids, it's hard with three, but even her going to the grocery store with me on a Sunday worked. Good luck, I hope she sleeps soon!