Faerie Solitaire

Barbie dreamhouse party

Cooking mama!

Try one of those so-called "casual games" from Gamehouse or PopCap. My mom liked Zuma the most. It's only 2.5 euro now in the sale.

Brothers - A Tale of two sons

Banished

What about some aventure games like Broken Sword or the Blackwell games? If she likes puzzles then I'd recommend Pandora's box. It's a microsoft-published puzzle game by Alexej Pazitnov, the creator of tetris. It's about pandora's box being open mixing the world up and the player has to travel around the world putting it back together. Every puzzle utilizes works of art and photography of local culture from each part of the world you travel to, and the music is also according to the local culture. It's not on steam however.

Bejewelled, Jewel Quest and these "Wow you got one!" games :D

Dwarf Fortress

[Insert Kappa here.]

Something with female protagonist, like Portal.

Skyrim

but no, probably some graphic adventure? they lack of everything but story and soundtrack.

Zuma, doesn't matter if it's the first or the second

To the moon would be a great game for your mom, it's easy (you practically don't need to do nothing), has a good story and a really nice OST.

Limbo

Little Inferno and Tales of Monkey Island

To the Moon

Possibly Solar 2 or Osmos? They aren't puzzle games, but they are calm.

Lucid
Lost Marbles
Thomas Was Alone
Strata
Girls Like Robots (Hopefully your mom does too ^^)
Super Puzzle Platformer Deluxe (Looks awesome)
Magical Drop V
Critter Crunch
More puzzle games and also on the side you can narrow down your search with other tags

I think trine 2 would be a good fit for her... it moves at your own pace, very simple in terms of combat and puzzle solving, and is very very forgiving if you oops and die. Plus it has multi player so I think she might get a kick of teaming up and trying various levels with you as well as solo.

I also think vessel would be a very good fit, its a puzzle game with slight plat former aspects. It's very simple to grasp and is another game you can play at your own pace, and both games have the option to save at will, which is huge when it comes to having to stop to do something else real quick.

I would also try the sims for her. It is not really a story based game, but I always told my fiance I love the sims because its like playing dolls but on a computer. Most females I have met tend to get a kick out of the game. I know my mom had her fun recreating our little family and trying to rebuild the house and everything lol. I know it seems silly but it was one of the first games that really got me into the whole computer gaming thing.

... and I know its been suggested and vetoed alot by you already but majority of popcap games tend to be a good transition for most people into computer games, for sure bejeweled, zuma, and bookworm all might be a winning download for your mother.

Oh I would also try scribblenauts... It's real cutesy in design and has ample freedom to both move at your own pace and is very simplistic in terms of progression. It allows you to play on your own creativity without really putting too many limitations on what you can and can't do.

plants vs zombies suits good in description.

Farm for your life? My mother loves games where you get to build and manage your own restaurant/farm/etc.

3d sex villa

Only game my mom ever liked was The Sims 2 and old Mario and Donkey Kong games.

My mom is a big fan of most of the games you can find on BigFish. Get your hands on the "big" ones and they are really really nice!