I recently bought an old hand crank Singer and because I'm right-handed it baffles me how people managed to sew with them in the old days. I wish I had some good ideas to help, but I think the main thing it will take is practice and working slowly. I imagine part of her problem is that it's not just a simple matter of changing sides, but there is the additional issue of keeping her body stable while she works. If the rest of us tried to work with the non-dominant hand and foot it wouldn't be the same because the other side would still be able to keep everything upright and balanced.
If she likes the computer, perhaps cruising through a site like Etsy or Pinterest will help her discover something she can try. As for doing puzzles, if she happens to like them, jigidi.com or thejigsawpuzzles.com offer some in a wide range of styles and levels of difficulty, without the inconvenience of having to dedicate a table to the project. It would probably be something that will help her to keep her mind active. She might also enjoy crossword puzzles online,
http://webcrosswords.com/daily-crossword-puzzles/ or Words with Friends (available via Facebook). You could play WwF with her - it's addictive!
My SIL's mom had a stroke at age 80 and was confined to a wheel chair for the rest of her life - 18 years! During that time we were amazed to see that she steadily
improved! She regained much of her ability to speak, which had been lost initially, and she never lost her sharp wit and ability to enjoy life and watch her grandchildren grow up. I hope your friend's future will be like that.