Can we write off our home- based business?

My mother is a registered physical therapist and works with disabled children at a local school. She also set up a Pilates studio in the basement of her home and has private clients daily. She has her business registered as an LLC and files taxes on her income appropriately. My question is whether she can write off the portion of her home that she uses as a business expense? Are there any stipulations in regards to runnning a business out of a residential home?