CBD currently does not have enough research to make many statements about its medical efficacy. The people in the shops who sell these products (now even at Macy's etc.) could be arrested for unauthorized practice of medicine. "This is good for pain, this is good for depression, this helps you go to sleep, this cures cancer, this will help your dog, this grows hair." At this point they are giving no more than the equivalent of quack medical advice. More research is needed into CBD and THC. This research was delayed for decades by its Class A schedule listing. My own suspicion is when they do enough research they will not find it to be the miracle drug many think it is.
Your sister's depression should be treated by a doctor, not a store clerk.