<i>Terraria</i> or <i>Starbound</i>, maybe? I mean, they're not "short", precisely, but they're open-ended, sandbox-type games (or Terraria is, anyway -- dunno about the other one), so, really, they're as long or as short as one decides. Also probably pretty good for co-op, if you and the missus want to play together.

Perhaps some good adventure games ? Shardlight, Blackwell, Primordia, Shadowgate, Edna & Harvey, Stick it to the Man, Jazzpunk, Grim Fandango are just some of my favourites.

Otherwise, perhaps Darkest Dungeon, The Witness, Don't Starve, Firewatch ...

Strip Twister.

https://www.youtube.com/watch?v=jqDGK_UjfFI

Be warned....

When a woman is into you, she will make an effort to get into, and come to like the games you like.

When a woman starts acting like those games are beneath her, she is probably also starting to think YOU are beneath her.

Its a very good relationship health test..... it also works both ways - if you find your not interested in trying to get into the things she likes, then its a clue that the effort your putting into the relationship is less than ideal.

Okay, as many people already mentioned, if she liked Plants vs. Zombies, then other Tower Defense games are a good starting point, and Defender's Quest is probably one of the best ones on GOG.com (and, could sneakily introduce her to some RPG elements :p).

Point'n'Clicks are also something she could probably enjoy. If she likes solving puzzles then go for Daedalic (Deponia series could offers hours of gameplay for example), if she's more into "interactive story" go for Telltale - they're all basically the same, so just go for the one with the theme she would enjoy the most (Walking Dead, Game of Thrones, Batman, Wallace & Gromit, Sam & Max).
Other than those, The Secret Files series is rather modern and pretty fun and Broken Sword could work as well.

Another genre that many people who are not "traditional" gaming types seem to enjoy is all sort of management games. Again, just go for the theme she would most likely enjoy - Civ, Tropico, Prison Architect, etc.
The Settlers series could also be a good choice.

EDIT: Of course, as several people already mentioned, I can imagine Stardew Valley would be a huge success.

Space Quest series - have her start with Space Quest 4 and 5, and if she likes those she can go play the first few ones (the first few ones are text based and not everyone's cup of tea).

Have her also try King's Quest 4, 5 and 6 if she ends up liking adventure games.