Florida appears to be a concealed carry state. Why didn't the lady, knowing the deanger of gators, apply for a concealed carry permit? I know gators aren't easy to kill but it would have at least been some defence that might have turned it away even with a non fatal shot. Gator hunters kill them with a .22lr, mostly to preserve the hide, albeit with a very precise shot. That said, I'm sure a large calibre such as .45, .357 or 10mm would have increased the chances with a less precise shot compared to the hunters favourite.
Also, on the common sense point, if you're old and maybe can't move quickly, why go right down to the waters edge? Would be better to walk 30 feet away further back to provide less of a target.
FInally as much as she might love her dog, sometimes its better to offer it up than become lunch yourslef.