I have two black sex links, look just like her. Cross between Rhode Island Red and Barred Rock, I believe. They are also called "Black Stars."
They lay medium brown eggs or lighter brown eggs, not sure which since their eggs are mixed in with my other birds. I would guess your lighter brown...
x2 on the Black Sex Link hen
My Welsummers lay eggs just like your very darkest speckled ones. Welsummers do tend to lay speckled eggs from my very limited experience with them (I have had a total of 4 of them through the years).
I have never had Cuckoo Marans- so I don't know what their...