Dimensional Warp doesn't change reality in anyway, it only distorts it. You can't rip holes in the fabric of space-time or anything like that. You aren't able to create things out of nothingness, or destroy anything into nothingness, nor can you reverse or travel in time, your ability to traverse space instantly is also dependent upon your knowledge and how much Lux favors you.

You are able to pinch space in order to cross gaps in it without actually travelling that distance, you can alter the pace of time. You can even bend and redirect vectors of forces and energy, such as curving the trajectory of a bullet or bending light around objects to make them look different/invisible and in extreme cases, you can warp actual objects, but you can't start or stop those forces or energies.

The Marked's application of Nullification is pretty situational here, it depends on what you're trying to do with your Warp. If you're trying to jump through space, the Marked can grab you by the arm and pull you out of the pinch (if she's fast enough). If you're trying to redirect forces or energies, she can touch those forces and energies to restore those forces to normal or even destroy them, since your ability creates a supernatural influence over them. If you try to swat a bullet that was fired at you and direct it at her, she can halt the bullet since the force pushing it is now supernatural, but if it was fired at her initially, she would have to block it by evoking hard stone or something.