Out-of-universe, when they made Man of Steel, DC weren't planning to pursue an expanded universe in the same way Marvel had, so Man of Steel was made as its own standalone film. When it turned out to be quite successful, it sparked the DCEU and Warner Bros started work on BvS. So the fact that Diana never showed up or helped out either when Clark crashed to Earth or when super-powered aliens invaded the planet is totally understandable OoU, because at the time it wasn't an Extended Universe.
However, I was wondering if, since Warner Bros have now opted to make the DCEU, there has been any reference or explanation as to what Diana's been up to since 1918?