Rin's backstory says that her arms had to be amputated, due to a birth-defect. However, if you've played Katawa Shoujo, you'd see she gets along just fine without them. Those feet of hers are incredibly prehensile, and she's really flexible. She can eat with them, open doors, and most importantly, she can draw/paint with them .
You're welcome, happy to be of service. Katawa Shoujo is a really fun game, and really touching too. I haven't gotten that far in the Rin's story yet, but so far, she has to be one of my favorites in the cast of girls you can end up with.