I don't think anyone was questioning whether the woman put up a good fight...
I think the wording of the article was in question, and looking at your link:
"Beneath the surface, the shark thrashed, whipping Halavais -- who at one point was on the shark's back. She fought the shark, grabbing and hitting it near its tail. Finally, it let go of her and vanished."
I've seen a few articles on the attack, and this is the MOST clarity I've seen, and even it seems to still be a little misleading. Others simply claim that the shark dragged her under and she beat on its tail until it released her.
If she was on the shark's back, she could have grabbed and hit it near the tail, which may have inspired it to try for easier prey and end the attack; however the wording "let go of her", "released her" and so forth imply that the woman was beating on and grabbing the shark's tail WHILE in its mouth, which, on a 14' GW, unless it was twisted into an "O" shape, would be something of a feat. It is also unlikely that the woman was on the shark's back AND in its mouth at the same precise moment in time.
By the article, she was in its mouth while on its back, and beat on its tail until it released her. This seems to require a woman who is between 9 and 14 feet tall. My guess is these events happened in some sort of sequence that is not being well-reported.
If she's claiming that while in its mouth, she was beating on its tail, it's also possible that she was grabbing and hitting at its dorsal or pectoral fins, which would be closer to the mouth, which might inspire it to "let her go", and she might have simply been mistaken, which would be understandable considering she was struggling for her life, not doing a dissertation on shark anatomy.
I suppose the shark could have also been twisted in a strange position, but would it have its tail sufficiently close to its mouth to have it beaten on, and would it continue to hold its tail near its mouth?
I'm not questioning the size of the shark, or the powerful struggle of the woman or, from the news story, the bravery of her friend and boyfriend. But since according to the news, sharks are vicious man-eaters, an uneven tan will get you bitten, and divers wear oxygen tanks, it's fair to assume the reports might be a bit off.