Fast pace: Quake 3 arena- The bots aren't smart, and it is an easy pick up and play, it teaches you to shoot on the move, retain accuracy, and expect anything
Slow pace: CS:S The bots are extreamly intelligent, and cheap, but it teaches you to keep your head down, and to anticipate situations before you even get on the battlefield.
OTHER-
Half Life 2: The combat is slightly difficult, but it isn't the biggest part of it, just make sure she isn't too frustrated on the physics puzzles.
Garry's Mod: You can set up the battles, and tailor it to her needs, like running, taking cover, ect.
Slow pace: CS:S The bots are extreamly intelligent, and cheap, but it teaches you to keep your head down, and to anticipate situations before you even get on the battlefield.
OTHER-
Half Life 2: The combat is slightly difficult, but it isn't the biggest part of it, just make sure she isn't too frustrated on the physics puzzles.
Garry's Mod: You can set up the battles, and tailor it to her needs, like running, taking cover, ect.