She's been planned as being there for a while. There's a lot of details in the world that are not shown as they don't come up in the viewpoints you (Shinji) tend to have access to. But yes, remember how in the AU she will likely be heading back to Japan in the next year or so? In this timeline, she left Hogwarts and came to Mahoutokoro, where the fox may or may not have introduced her to the young Fujou head. (The engagement is recent, as of a couple weeks ago).
As ever, I am happy to answer questions here or discuss more on IRC, if you'd like to know a bit more.