Music!!!! I had a screamer too, lasted 6 months. During naptime I would put my ipod on either on the dock and play it throughout the house or use my headphones and just watch the nappers on the monitor.
If she is screaming during playtime/circle time etc try music. My guys all love to dance and jump around and 'sing'. Music is my stress relief so I always try it with the kids too. Some days the music is on in the background for our entire day. Some days we play kids songs other days stuff I want to listen too(monitored of course for swearing etc)
It was honestly the only way I got through it...I wanted to terminate so many times but held on because her family was awesome and they were trying just as hard as I was. It did take forever but she then ended up being one of my favourite daycare kids of all time (not that we have favourites lol). I was sad when she graduated out of my program for school!