Point and click adventures that aren't too difficult. The Longest Journey, Broken Sword, Book of Unwritten Tales, Syberia.

Civilization 5 because it's accessible and the concept is epic

Heavy Rain if you have a PS3/4 or emulator.

I wonder why nobody yet mentioned The Incredible Machine. Best puzzle game ever.

Honestly, I think most of the responses in the thread are based on a faulty premise that games for a nongamer should necessarily be easy and/or low-investment. What sort of non-videogame content does your wife like? Does she read any books? watch any series?

E. g.
crappy YA novels -> Dragon Age, Masquerada, Valhalla
stylish fighting anime -> Hyper Light Drifter
Stranger Things -> Oxenfree
Vikings -> King of Dragon Pass, Banner Saga
Game of Thrones -> Crusader Kings 2, The Witcher
Walking Dead -> Project Zomboid
Orange is the New Black -> Prison Architect

The only requirement I think stands is that at no point she should end up having wasted her time, so no roguelikes and no games which become unwinnable long before the actual game over.

My girlfriend doesn't really play any games but she likes Phantasmagoria 2, so make of that what you will.

Get some demos. That's how my wife figures out what she likes. Bigfishgames has lots of demos.

PS my wife loved the Drawn games (painted tower is the first one). It's her favorite.

Another vote for Defender's Quest and Stardew Valley (although SV may be a little too long).

Also, World of Goo fits---quirky, not too long, not an RPG, easy-to-learn gameplay.

I got some girls into gaming with World of Goo and Braid as well as with Flatout 2 and Blur.
For some reason the most popular game for my ex-gfs was Knights of Honor though, which is a fairly authentic and advanced strategy/politics game set in medieval times.

And then there's World of Warcraft and The Sims but I don't like to talk about that...

"Brothers: A Tale of Two Sons" might be interesting for her. Although for non-gamers I've seen it can sometimes be hard to really empathize with the characters. They don't really immerse themselves much. Her enjoyment of the game will depend on this.

If you are looking for co-op games, "Lovers in a Dangerous Spacetime" and " Keep Talking and Nobody Explodes!" are both pretty quirky and interesting and are on sale on Steam right now.

If she wants something with less gameplay but a bit more out there in concept "The Stanley Parable" is easy to play and is the sort of game anyone can get where its charm lies regardless of past experience with games, though it certainly helps.

Finally, "Scribblenauts" is a puzzle game done in short bursts, I can see two people having fun together brainstorming solutions and trying to guess how many different things the game will allow them to create.

Stick It To The Man!

[EDIT]

Also, Owlboy.

TIS-100

If she likes the Walking Dead series, wouldn't the actual Walking Dead games be a better choice? Aside from being closer to the series/ comics, they also have very simple gameplay and focus on story, so that might be a plus if she's not much of a "gamer".

Here's another vote for Stardew Valley and the Kingdom Rush games.

Hmmm... I'd say it's far closer to some mobile TD games vibe than PvZ. Quite difficult. Pushing to 60+ seconds is difficult for the first two levels nevermind their super versions... Hmmm.. does she like...
Story driven?
Action?
Arcade?
Puzzle?
(Not RPG, probably not FPS)
Hidden puzzle?
Idle?
Tower Defense? (yes apparently to some degree)
Horror?
Idle/Time Wasters?
Rogue-likes?
Point&Clicks?
Management?
Space games?
Flight games?
Simulators?


Hmmm... Might consider:

Doodle God/Devil (android-ish game, on HB)
Little Inferno
Reccetear (Manage a shop)
Triple Town (nearby match-3, upgrades)
Unmechanical (puzzle, physics)
Journey to the heart of Gaia (puzzle & Hidden object, on HB)
Knights of Pen & Paper (Semi-satire D&D game)
Concrete Jungle (city management/building/card game/puzzle, Steam/HB?)

Hmmm not a lot to recommend for 'short games' really...

Braveland is not very long and very approachable for casual gamers. And if she likes this one, there are two more: Braveland Wizard and Braveland Pirate.

The Broken Sword series is really good.