First of all, it was an interview, not a presentation or a lecture by the author. She didn't get to pick and choose what she talked about. She was asked questions, to which she responded. It is much the same, in that respect, as it was for me on Issues, Etc. There were a lot of things that I would have preferred to discuss, but the callers had other things in mind, like it or not.
Along similar lines, it was very obvious that Dateline did a good deal of cutting and editing in putting together what was aired on t.v. That's not a criticism, but simply an observation that what the audience saw and heard was what the producers considered to be most important and interesting. Whether that reflects the author's own priorities is questionable.
What I had not gathered from the comments I was hearing about the show, nor would I have guessed it, was that Rowling was doing her best to avoid giving too much away, since the group of children who were meeting with her in Scotland had not all completed the seventh book. There were spoilers, to be sure, but even most of those were fairly general and as vague as Rowling could make them. She has repeatedly made it clear that she very much wanted her readers to reach the ending for themselves, and not to have the climax ruined for them.
A particular case in point was the one question she was asked, specifically, about the religious themes of the book. She responded that, of course, the religious themes are prominent and, in her opinion, quite obvious by the time you reach the end. She reiterated what she has said in the past, that an awareness of those religious elements would have given away a huge clue to the conclusion of the story. It was evident in her reply that the religious aspects were intentional, and not incidental but an important part of the entire enterprise. Nevertheless, she did not elaborate or go on at any great length (at least not in what was aired on the Dateline interview), partly because her books are the way that she, as an author, has communicated her thoughts on these very matters, and, again, because she didn't want to "spoil" the ending by spelling it out.
A major purpose of the series, as anyone who has read the books will have figured out, is to grapple with the way that a person approaches death and deals with death. I gather that would have been true to some extent, in any case, but it became all the more pronounced with the death of Rowling's mother (at age 45, from multiple sclerosis) within months of beginning to write the first book. After that, she found that the books became a major outlet for her own wrestling with that loss in her life. I found it interesting that when she alluded to her faith in the life after death, she hinted at the different beliefs that people have in that regard, and she intimated that, if readers were aware of her own particular faith, they would have been able to guess how the story would end.
Some viewers may have been put off by her comment that her religious struggles are often a struggle to keep believing. The interviewer acted a bit surprised by that comment, anyway. Yet, this is exactly the experience of any Christian living under the cross. I thought it was an honest answer, even if I would have been pleased to hear her make some confession of the sure and certain hope that is ours in Christ. Again, she communicates the triumph of her faith, if you will, in the midst of her struggles, by the outcome of the books that she has written. Along the way, Harry's doubts and struggles, his ups and downs, his falls and perseverance, are echoes of her own journey (one that is frankly not so different than my own, in that respect).
On a side note, this is one of the reasons that I have never viewed Harry Potter as a "Jesus figure," per se, but as one who is catechized to live and walk in the pattern of Christ, conformed to His image by way of repentance and faith. I doubt very much that Rowling would put it this way, but to me it has always seemed a visual portrait of the daily significance of Holy Baptism, the dying and rising of contrition, repentance, and faith in the forgiveness of sins, whereby the New Man arises in us to live before God in righteousness and purity forever.
Along those same lines, I really perked up when Rowling commented on the one last chance that Voldemort had remaining to him, in the end. In the book, Harry pleads with him to find some remorse, and I have previously asserted that one should understand this "remorse" as a description of repentance. Well, sure enough, when Rowling talked about this point, she didn't use the word "remorse," but specifically said that Voldemort had that opportunity to repent. In some ways, I found that single word from her lips to be one of the most telling of the interview.
Finally, I was particularly touched by Rowling's comments on the differences between Fred and George, and how those distinctions figured in her decision to have Fred killed in The Deathly Hallows. For her to "know" those twins so well, and to have such a clear mental picture of their respective individual personalities, is no doubt a major factor in her masterful and compelling development of all the characters in her story. That's not a religious factor, but it is brilliant.