She has a Portal Gun that spits out blue and orange ends of a portal. They don't have to be on the same orientation, but they have to stick to walls, not free-float- And they're always the same size, and only white walls.
The challenges involve things like getting around beams of radiant damage, or redirecting them into targets in order to open a locked door, or moving spheres and cubes and beams around through creative portal use. They're not nearly as flexible as his portals, aside from the bits where they can be different orientations (leaving a cube bouncing up and down in two side by side portals, once), and how you can move one end independently of the other.
Also, there's a disembodied voice sarcastically threatening, joking, or insulting with the player as she progresses. The production value of the illusion is pretty good. The music, too.
"It's all a big puzzle, really. Do you want to try? There's a two-player mode, I never did much of it."