Derek,
I would say that the first 2 pictures were building, as her tail doesn't look like it is "sucked in" enough. I can't really see the tail real well in the last pic, but it definitely looks more like an ovulation. One thing I do if I am in doubt, is to gently pick up the swelled area, and squeeze (not like you are palpating, but gently). If the area is slightly soft, it is probably just a build, however, if it feels like a rock in there, you can bank on ovulation.