So... why did this happen? What was going on? Was there a point to this bizarre drama scenario? Don't get me wrong, I'm very glad to have a happy ending because this series is a happy series and it needs a happy ending.
However, because of that it doesn't make sense to have this strange drama scenario and have it go nowhere. We didn't learn anything about Mahoro's powers, there was nothing new about her grandmother or really about anything. It just feels like the author had felt the sudden need to try and scare people at the end, and then went "just kidding!"
Really, it feels like the sort of ending you get when a series is axed, so despite what the author said, I am very suspicious that that is what really happened.