My wife was a Coors Light girl when I met her. But after I brewed a lightly hopped Blonde Ale for her... she was hooked on craft beer. Now she loves, Wheat beers, and Pale Ales. I have slowly, over the last 2 years, added more and more hops to the beers I brew for her. Nothing too crazy, but she is becoming more tolerable to hop flavors.
Brew your sis a good light colored and lightly hopped ale and she will be hooked as well.