That is sandy recessive white which is different from the normal recessive white. This could be a great opportunity to experiment with her to see how it acts with the other colors. Are you planning on using this pullet somewhere in your breeding program?
Sandy recessive doesn't cover all the red for some reason of which I have not yet fully figured out, I'm working on understanding it more fully. It doesn't seem to be a fully understood gene.
Regular recessive white covers all color in it's purest white form, ie. . . (selectively bred for).
I'm not an expert on Red Shouldered Yokahama. They have at the very least a form of this sandy recessive white.