Neither, it's an old wound. For the record, though, C-section would be lower and more central. An appendectomy would be more to her side, I believe. Also, both would be much less ragged, due to professional suturing.
I have a _very_ hard time believing that this pic features a "flat chest." Maybe the character normally does have one, but in this picture, it looks like a good-sized chest flattened only somewhat by gravity.
