Some of the Big Fish games are really good and they are all more or less targeted towards women.
"4 Elements" and some of the farm games are not bad.

Nice recommendations Melhelix, a few there that I didn't know about but have me interested. In particular, Driftmoon, Emerald City, and Enclave.

If we are going with BFG I would have to put my vote in for the Mystery Case Files series (with the huge exception of Shadow Lake -- Sucked worse then a 3rd rate hooker)

How about CSI - http://store.steampowered.com/app/21730/

Can never go wrong with some Bejeweled!

Defender's Quest and Rogue Legacy are your best bets .

My favorite ones (all can be found here on GOG):

Driftmoon - Laid back RPG and very fun game, not too complex and many stuff to do.

Spelunky - Roguelike game with the (one more round) effect. I play this a lot when I'm not in the mood for serious games.

Trine 1 + 2 - Sidescroller games, fun and simple. Comes with a few puzzle across every level and a simple story.

Don't Starve - Survival Sim, your goal is to survive for as long as possible by picking materials, building weapons, campfires, can become highly addicting.

^is right

Have her look through the GOG adventure games - http://www.gog.com/games/adventure

Get her hooked here. Some maybe a little more thought needed then casual but being a point click junky when the genre died out for a bit I had to try the causal to help fill some voided time..

I am not sure it is still going but I also used to go to AGS http://www.adventuregamestudio.co.uk/ and check out the games there.

Angelica Weaver: Catch Me When You Can and Nightmares from the Deep: The Cursed Heart are solid Hidden Object games that I played through and enjoyed (as someone not too fond of the genre). No idea how they would compare to Castle and if she'd be interested in their stories, they don't allow you to skip puzzles, as far as I remember, but they have hints systems to help you in-game so you don't need to search for walkthroughs.

I also tried Dracula: Love Kills for a bit, but found it too cheesy and production values too low compared to the two above (mostly because of the awkward intro movie - which is in a different style than the rest of the game - and because of the bad voice acting; I admit I haven't played it for long).

If she liked the storytelling of Castle and the HOG mechanics and puzzles aren't that important to her, depending on her taste in movies, maybe she would also like interactive story games like The Walking Dead or The Wolf Among Us?

This might be a little too convoluted, but what about a point-n-click adventure game like Tales of Monkey Island or the free Flight of the Amazon Queen?

They requires a bit of investment (puzzles puzzles puzzles), but both have a fairly friendly interface.

I won't disagree with Defender's Quest, especially if you only select the "casual mode" levels. (Each stage gives you difficulty options.)

If you can list a bunch of platforms, I'd gladly suggest Robotek and other free Android games.

Very true!

More great casual games:

Alchemy, Chuzzle, Peggle, Slingo (especially the Egyptian one), Bookworm & Bookworm Adventures, DaVinci's Secret, Snood, Plants vs Zombies (original), Crystal Path, Adventure Inlay/Magic Inlay/Puzzle Inlay, Inspector Parker, Ricochet, Peggle, Angry Birds, Pandora's Box (this is a classic!)

More great Hidden Object series:

Midnight Mysteries, Mystery Case Files, Mystery P.I., Little Shop (series), Big City Adventures, Magician's Handbook, House of 1000 Doors, Drawn the Painted Tower, Dream Chronicles, Hidden Expeditions, Mortimer Becket, Miss Teri Tale, several Agatha Christie, Sherlock Holmes, & Nancy Drew crossovers (adventures/Hidden Object), The Magician's Handbook, and whatever else BigFish recommends this week lol

Some possibly helpful inks ~

http://www.gamezebo.com/2012/05/11/gamezebo-readers-pick-their-favorite-hidden-object-games/
http://jayisgames.com/best-of/2012/
http://internetgames.about.com/od/webgames/tp/hiddenobjectgames.htm

<(")

Ones my girlfriend plays all the time:
http://store.steampowered.com/app/236290/
http://store.steampowered.com/app/3620/
http://store.steampowered.com/app/15900/
http://store.steampowered.com/app/29120/

Basically, have a look at Big Fish Games =). Their main seller is Hidden Object games (basically the genre you described). Nearly every game comes with a one hour trial so it's great for finding new stuff. No need to join up if you don't want to. Although doing so does get a bit of a discount (but then again, you can join up, get the members discount, then cancel in the same month -- something I do fairly often these days).

Oops, nm, might not be enough in the casual vein....

Planescape: Torment. :P

or

Don't Starve
Sword of the Stars: The Pit
Zafehouse: Diaries