You can laugh at this if you want but...buy her a guitar or ukulele. It's fun, and it doesn't matter what age you are. Anyone can learn. There are tutorials all over YouTube...good ones. I use them all the time for different solo pieces, etc.
Fourteen years ago, I underwent two back surgeries. After each, I spent at least a week, prostate on a couch, too doped up with painkillers to do much of anything. What did i do for amusement? I watched tv! Something I'd rarely done in the preceding twenty years! And I discovered it had only gotten worse over that time! But I did learn to use the channel-flicker gadget! But tv aside, there are loads of free browser games on the internet. And there are crossword puzzles to work. And she could always come on this site, to vent her aggravations!
Oh your poor sister!! Hope she has a laptop, plenty of distraction online, Solitaire is a good one for me. I also knit, crochet, cross stitch, I've tried tatting (that made me kinda crazy, I needed a personal demonstration), good books, and if all else fails Cable TV as long as it isn't Faux News.
When I broke my leg in high school, I knitted a sweater and read books for six weeks. I love watching Netflix now and talking about the things my friends and I see. We recommend our favorites to each other. Playing dominoes or other games stimulates conversation among friends. You could go on excursions--maybe a picnic. I highly recommend reading books for the challenge--a productive pastime ideal for when you aren't attempting something a tad more active. I know safe healing is important.