Doug Otte wrote:
Roddenberry was upset that she was leaving, so had her character killed to avoid any possibility of her coming back.
Are you sure about that? When her character was brought back, it was in the third season, and Roddenberry, though not running the day-to-day operations, was still very much involved in reviewing the scripts and giving his approval. I base that on the fact that Michael Piller did not join the staff until the third season, but talks about the conversations he had with Roddenberry where Roddenberry was unhappy with a particular script and they had to rewrite it.
Yes; I'm sure about it, but not sure where I read it. Maybe it was in Engel's biography.
However, I can't explain about her reappearance in Yesterday's Enterprise. I think, by that time, Roddenberry was pretty uncommunicative, and so didn't have much input into the show. Any quotes from the cast and crew to the contrary were probably just propaganda for the fans.