The new lady said no. She then offered to switch her middle seat with the man on the aisle, but the other lady said but that's his seat not mine, referring to the man already sitting in the aisle. The new lady said too bad then and proceeded to make the other lady switch and sat next to the other lady's husband for the 4+ hour flight.
I spent way too much time trying to figure out why she wouldn't switch. There was no benefit to her that I could see to being in 14 instead of 15. Neither were exit rows. She wouldn't get off the plane the one row sooner since her bag was up in the back, and she would have to wait until everyone un-boarded to get it. There were no babies, and the men in 14 were even larger than the men in 15, which does matter when you are spending hours crammed next to a stranger and want to preserve all the personal space you can.
I can think of a few reasons someone wouldn't want to change, if they are sitting next to someone with them (she wasn't), if they are asked to switch an aisle or window for a middle (which I have done before for people if they are nice), or maybe even if they are way up in the front and are asked to go way back in the back of the plane (this was one row).
The only thing I can figure is that even though there was no benefit to her to keeping her original seat, there was no benefit not to. She was not willing to do it precisely because it benefitted the someone else and not her. Something so simple that would greatly improve 2 people's next few hours and not hurt you at all. She didn't do it because she didn't have to. I hope there are not too many people like that in the world, but I'm scared that there are.