I would say you have a cross. A cross between a wheaten Marans and a RSL of some type would probably give you a bird like this. Unfortunately, with crosses, it can be impossible to tell you what two breeds were crossed. Add to that the fact that RSL aren't a breed at all, but crosses themselves, and you could have quite a messy genetic stew there.
But, she is very pretty and it sounds as if she lays a gorgeous egg. I have some blue copper Marans pullets that are 19 weeks old this week, and I am going crazy looking for my first dark egg!