So I guess that instead of worrying about her arthritis, I should
hope she doesn't develop carpal tunnel syndrome! I always hold
(held...) my XT by the grip and sustained the bottom with my pinky. I
don't see how holding the camera in the palm of the other hand can be
comfortable, especially if she uses the Live View to compose her
shot. Her wrist would be backward bent 45 degrees.
Unfortunately, there are a lot of people who don't know how to properly hold an SLR. The left hand has long been the supporter of most of the weight of an SLR, and it also is used to turn the focus/zoom ring of the lens. And you won't get tunnel carpel syndrome because the internal wrist muscles are not being contracted. They remain relaxed.
People who support the camera with their right hand, by grasping the grip put much more pressure and exertion on the muscles of their hand and wrist because in order to maintain that grip, the muscles need to maintain a state of contraction. It is repetitive contraction of the wrist muscles that causes tunnel carpal syndrome. That's how people who click a computer mouse all day long, or type all day long, get tunnel carpal syndrome. Repetitive contraction of those muscles, even if it just means just depressing a mouse button or a keyboard key, is what leads to tunnel carpal syndrome. When you are using the left hand as an open-palmed, relaxed support for your camera, there isn't really any muscle contraction. And, in fact, the muscles are doing the opposite of contraction. They are doing muscle extension, ie. muscle stretching which, by the way, is an aspect of treatment for those suffering from tunnel carpal syndrome, and is often recommended for the prevention of tunnel carpal syndrome-- stretching exercises to prevent tunnel carpal syndrome. Frankly, we should all stretch more often.
By supporting the weight of your camera with your left hand, with your left hand being relaxed in an open-palm manner, you can comfortably hold not just light cameras, but also heavier camera/lenses. Here's a photo of my friend shooting with the large Canon 100-400L IS mounted to her Rebel XT (a lens which, as you can see, dwarfs the compact Canon Rebel XT). She is exhibiting proper, relaxed hand-holding technique. Not only is here left hand relaxed, but her right hand is relaxed, too. And she can shoot with this relatively bulky rig all day long, with no hand fatigue because there's practically there's hardly any
gripping or contraction of hand-wrist muscles. So whether you are arthritic or have practically no muscle strength in your hands/wrists, you can still shoot with an SLR (even a heavier SLR) with this relaxed hand-holding technique.
But hey, if you want to recommend to your mother that the only way to support a camera is by grasping the grip tightly, they go ahead. She's your mother. No need to listen to many of us, who've been shooting for years (decades, even), and have perfectly healthy wrists and hands, in spite of countless hours of shooting with our cameras.
