Because of the leg color, I really don't think she is a BR and RIR cross. Those legs should be yellow, not black. I can't tell all that well from the photo, but her beak looks like it is maybe black with an ivory-colored tip. My Speckled Sussex Rooster over Black Australorp cross hens have...
It depends on what breeds are used to make the Black Sex Link. If the father is a red bird, yes, there is a good chance that the BSL hen will have red or brown around the neck. Roosters other than red or brown will give different results.
I do not agree that it has to be a Black Sex Link. It...