Her character stands as a benevolent leader and role model.  For her subjects.  She has been portrayed as going to extreme lengths in order to protect her subjects, or her position depending on how you view a scene.  

In the scene in which the blog is at now Celestia is alone with her aide, and the Queens whom have openly invaded Canterlot and whom are of a race that Celestia considers socially and cognitively inferior, as well as highly destructive.  These are views that she has held for a long time, and that have been reaffirmed by Chrysalis.

In the blog Celestia openly says that she will strike down the changelings, which she views as a threat, to protect her citizens as she has done before.  She is looking out for her own kind.  She is also the first to initiate action in such a confrontation, as she has done before.  IN CANON.  Her reasons for attacking Chrysalis were well founded and supported, but at the time Chrysalis was alone.  Celestia was the first to take direct action in that confrontation, not Chrysalis.  Celestia shot first, and that is what she is doing now.

Celestia is not ‘openly genocidal’, she is genocidal behind closed doors and only with those that she trusts greatly, such as a personal aide and secretary like Raven.  If I have failed to portray that by having the throne room be almost completely empty, save for the aforementioned parties, then I apologize.

If you follow a story blog, watch a movie, read a book, whatever, trust its writer.  They have reasons for doing what they do, and those reasons are rarely out in the open from the start.  If they are, then they are doing a poor job of telling the story.