She, and the castle both. I mean, the castle is inanimate. Over how-many-years it has, or should have , built up some sentience. But I can see how it would have a very single-track mind about these things, and view Snape's actions as "breach of contract" ("oh, and, thanks for the hole in the window, pal, that used to be a nice one") and thus refuse to provide him a portrait. Sure. Maybe I can rationalize that. This isn't in the book, obviously; it's only from interview that I infer this. And if JKR were saying "well, the castle thought this", then sure, maybe. But she herself appears to agree, which makes me raise an eyebrow at the very least.