Hina got Shirosakura in Chapter 258. As for your other question, I'm not sure myself. I think it might be related in some way to the Royal Garden or something like that. We should hopefully get our answer after this current story arc.
I believe it was implied that the god Athena made angry was King Midas. Answering your second question, how she made him angry was due to the role she played with Mikado and Himegami ten years ago when they where in pursuit of God's power/power of royalty.
Thanks for the reply...
I'm closing this, seeing that the question on this thread has been answered.