I'm inclined to believe both of the images are of Nancy, though naturally cannot say anything for sure. In any case, here is what I think happened.
Nancy had had moderately large implants (from the mainstream point of view) for many years. For what ever reason it had become time for some revision. She had enjoyed being busty so much that she was interested in going further and ”dramatically increasing her breast size”. She looked for and found a plastic surgeon capable of working with larger breast implants. The doctor however was located far away in California. The distance didn't discourage her though, and she travelled all the way from the East Coast to see the doctor on the West Coast.
The image on the left side was taken before the surgery to insert the larger implants. The operation went well, and she soon traveled thousands of miles back home. As far as I have understood (correct me if I'm wrong), her current implants are expandables. Adding saline is a simpler thing to do than more invasive procedures, so a local plastic surgeon could do it. Quickly her breasts were really pumped up in volume.
Again many years passed, and her chest gradually became more saggy and low hanging. I like to think a lot of bouncing contributed to it – be it at say car show with her and her husband smiling the more shocked people were at seeing her undulating mass of enhanced femininity, or at a more private setting at home. Perhaps it was merely because of the weight of the implants and gravity. To mitigate the sagginess, it was time for some more surgical revision, and once more she travelled to California to see the doctor.
The image on the right was snapped before a breast lift surgery. Again the operation went well, and she returned home after recuperating for a short while.
In this scenario, there are several years between the pictures, and the result image has been taken a long time after the enlargement procedure, and on the other hand right before a breast lift operation. The time difference accounts for the somewhat different looking freckles (though I think there are similarities), and the relative sagginess displayed in the after image. As for the ”fat” arm, perhaps its just a different position she is taking, but there are also some images where she is noticeably heavier than usually. Its perfectly normal for people to sometimes gain weight and then lose it later.