Eddy said it, but doesn't mean that this is the case. The writers make many mistakes and failed plots,Ā but being presumptuous doesn't make you right.
If they say that they originally planned her to be the stepsister, then that'll be proof. If they never get to Ana's story, there'll be lost potential. The audience isn't all knowing and they certaintly do not decide the plot.
As I said, if they wanted her in the story whether they got the actress or not, nothing stopped them from doing so. So clearly, they had other plans. If we entertain the idea that "they changed their mind", then at the very least they were going with their original plan keeping much of 104 intact.
Would it have been cool to see the Ana tie-in? Yes, but it doesn't mean that that they go out of their way to roundaboutly enact a story that they created for "reasons". I think they are pretty average writers and somewhat sporatic showrunners that tend to have a lot of lost potential, but I think in this case that they aren't the villains you make them out to be.