Somebody is definitely going to say it...so let me get it out of the way. There is no "mound" in softball!
If you are refering to the pitcher's plate, that little white rubber slab is totally irrelevent to the Look Back Rule. The pitcher is either within the circle or she is not. When she is, and she is not making a play, any runner stopped on a base may not leave it.
This is a LBR violation. Dead ball, runner out.