Crochet tends to be a more open stitch and knitting less so unless you needles larger than suggested for your yarn. It's personal choice. My choice is knitting although I can do both if I have to.
This is an excellent scarf to start with and is only knit and purl and can really use any yarn with an appropriate size needle. I suggest worsted weight and size 8 needles.
Cashmere and merino are good, but if she's extremely sensitive skinned even some of those may be itchy. I've been searching for one I can wear and so far it's a no go. I tend to stay with a very good acrylic,
Cotton, bamboo, and silk. Usually one or more of them blended rather than alone.