Assuming preboot Diana, Sandman only has his own sandmass under control?
Diana.
Assuming preboot Diana, Sandman has entirety of desert's sandmass under control?
Sandman.
Assuming preboot Diana, Sandman only has his own sandmass under control, Diana uses lightning cuff ability?
Diana wins quickly and easily.
Sandman incapacitated.
Gets turned to glass.
See Sandman versus Doctor Octopus.
Assuming preboot Diana, Sandmas has entirety of desert's sandmass under control, Diana uses lightning cuff ability?
Don't know. Inclined toward Sandman. Answer might depend on how large desert is. Preboot Diana is very strong. And very fast.
But she still needs to breathe.
See Sandman trapping her long enough to make her pass out from lack of oxygen.
DCnU Diana loses to Sandman if Sandman has desert mass to control.
7 or 8 out of 10 shot of victory if Sandman has only himself, owing to Diana's unfamiliarity with fighting this type of opponent.
Needs to allow herself to be physical in the way a Hulk might act.
Thunderclaps and hurricane force exhalations are far likelier to win than even the most skillful swordplay here.
1. Required fissionable radioactive material. Diana had that in Superman/Wonder Woman #6. She and Clark were in a repository of Uranium-235.
She doesn't have that kind of material here.
2. Required concentration, fine motor control, and the ability to SEE down to the atomic level. The odds against her cleaving atomic particles without this, even in a comicbook, are astronomical.
3. Nearly killed Wonder Woman AND Superman. DCnU Diana, strong though she may be, has demonstrated nothing on the level of preboot Diana's resistance to explosions.