1 And now that a month has passed, she decided to write a review.
2 And now that a month has passed, she has decided to write a review.
3 And then that a month had passed, she decided to write a review.
I am pretty sure that 2 is correct. But I don't think it fits the idea of her having written a review already. If she has written it yet, her decision is no longer connected with the present. Which makes 1 correct. But I am not sure.
What about 3?