So sorry your sister has had a rough go, Julie!
We were told that the first year is indeed the most critical and the most difficult. It seems that it is a continuous process of tweaking the medication, dealing with side effects, and the body, just in general, adjusting to the new kidney and all the medications.
Hopefully things will continue to resolve for her as time goes on.
Julie, do you think she would allow you to go with her to one of her doctor visits? If she doesn't mind, it might make you feel better to hear what is being said and to know that the doctors have things under control and are looking out for her welfare. I know it helped me to feel like I had a better understanding of what was going on, and to serve as that second set of eyes and ears.
Best of luck to you both!