Well, if you wanna be that complex...
The B***h fortifies her void dragon, and cloaks it in space-time. She then touches it, and puts immutable space-time portals under each of its scales, each of which leads to the pits of Tartarus.
Around her, she causes light, space and gravity to dilate to extremely high mass, to form a wormhole that serves as both a forcefield, and a portal to any destination she chooses. From this spherical portal, monsters, beasts and demons can easily enter and exit at will. And if she wants, she can adjoin it to other locations, to let out the dangers on the other sides (like opening it up to the surface of the sun, or to the bottom of the ocean.
It's both a forcefield and a gate to other locations and times.
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)