No physical issue, she just decided that she wanted/was entitled to my seat. Unfortunately, I think it would have caused a prolonged incident if I had made an issue out of it as selfish woman wasn't budging. I like my window seat too (especially to/from NZ), so all in all, I think the cabin crew could have been a little bit more grateful for my willingness to move. Ah well.
The way I've handled this in the past is something to the effect of lets compare boarding passes, or something that encourages them to get out the boarding pass and show me. So far its managed to move even stubborn passengers. I've never had a flight attendant overrule me though. Which as previously mentioned, all air crew directions have to be followed and once they do that its game over.