Well, if that's the case, she started working on said fulfillment way back in Book Four, which is when it became pretty clear to me that they were going to end up together.
Rowling says that she should have put Hermione and Harry together in the Harry Potter series instead of Hermione and Ron, according to the publication’s headline, which reads, “JK admits Hermione should have wed Harry.”
I mean, I don't doubt that she's being truthful about feeling differently about it now, but short of writing a sequel in which they're all middle-aged divorcees, there's really nothing to be done about it.
(Anyway, I've always LIKED Ron and Hermione together. And it should be noted that Hermione didn't HAVE to end up with anyone!)