I agree with dirtfarmer. A trackball is the only way to go. I am amazed at how few people use them. You can get them wireless and then hold it wherever is comfortable for you.
At my son's wedding we bought a ton of disposal cameras, handed them out to closer friends at the reception with the instructions to pass it on to someone else when done. We had a drop box for the fully used cameras. The pix we got were priceless. We got very few not returned or not full. Well worth the expense of the disposables.
Check out the Sony "High Zoom Point and Shoot" type of camera. Has all you are looking for plus a decent zoom for a point and shoot. Has all the settings from manual to compete auto. Burst in 2 modes - 10 pix in one second or 10 pix in 10 seconds. You also get the added benefit of putting it in your pocket with no hassle. They run on their own rechargeable Sony or equivalent batteries. Regardless of what she ends up with, always have her carry extra batteries and an extra memory card.