Anyone make an arm sling before? Sewing Machines Parts and Sales in Los Angeles

My 2 year old daughter fell today and broke her collar bone. She was prescribed a sling for 4 weeks. The sling they provided is way too big and is chaffing her neck. I’m think of deconstructing it and making it smaller but was wondering if anyone has ever made one before. I have a ton of scrap fabric in cutesy patterns she’d love.