Ixnay on the G12, although I am a Canon guy... its just too dated looking, and I'll leave it at that.
My first question to you is... Is this for you or for her? Really, now.
Next question, will she want a big clunky camera like you're looking at, or a true point and shoot, which is smaller and more purse size. I prefer the later. If I want a big camera I'll just use my video camera.
My point and shoot is a Canon A590is
http://www.steves-digicams.com/camera-reviews/canon/powershot-a590-is/canon-powershot-a590-is-review.html#bby the way, I like that steves digicam site for reviews as well as cnet and a few others.
My video camera is a Canon Vixia HF s30
http://www.usa.canon.com/cusa/consumer/products/camcorders/consumer_camcorders/vixia_hf_s30... and my favorite thing about canon? CHDK (Canon Hack Development Kit)
It turned my a590is almost into a DSLR, with obvious differences in final picture quality, but it added so many functions like time-lapse, bracketing, super slow and ultra fast exposures, motion sensing, and on and on.
Here are some sites to look at...
http://lifehacker.com/387380/turn-your-point+and+shoot-into-a-super+camerahttp://hackaday.com/2008/05/27/how-to-expand-your-camera-with-chdk/http://chdk.wikia.com/wiki/CHDKhttp://chdk.wikia.com/wiki/CHDK_for_DummiesI just wish there was a hack for my video camera as it is already badass. I don't use it enough though. Its the first time I've ever spent $800 on anything other than cars and bikes, it makes it hard to take off of its pedestal, lol. Also, when I say hack, its not really a hack. Its a firmware mod via the sd card, once you take the sd card back out, camera is back to stock spec, so no voided warranty. Speaking of Canon warranty, they replaced the lens on my a590is for free after 6 months, and also sent me a free remote for my camcorder when it wasn't included in my ebay purchase from a private seller.
The A590is has been thru a LOT! I've used it on the front of my helmet for nearly 4 years now. Look around on this site enough and you'll see a lot of videos and pictures I've taken with it. Godzilla, Old Bike Ride, etc. I've actually considered buying another one, even though it is a 4 year old design. I love the weight and feel of it, as well as the capabilities. I've just destroyed the lens on mine. OH! that reminds me, it is one of the only point and shoots you will find that has optional lenses! they just fit over the auto zoom lens, and give you macro, wide field, zoom, filters etc. I really wish I'd figured that out before destroying the second lens with it on the front of my helmet all these years.
Of your choices, I would choose the sx40 or the Nikon. I think it would behoove you to look at some smaller cameras though, for the missus' sake.