I'd consider what kind of game she finds fun and compelling--that's more likely to engage her to become familiar with the mouse/keyboard combo.
That being said, Minecraft on peaceful mode would fit and is generally approachable. Stardew Valley is pretty relaxed as well, though I don't remember whether it uses WASD specifically.
Oh! And if she's into puzzles, look at Islands of Insight. First person with puzzle solving as the main mechanic, but also some exploration and a bit of mystery to it.