I think that is a process, and takes time and life experience, to learn critical thinking. It comes from being in the world and being exposed to different things and people. I definitely don’t think it is your sole responsibility to teach your sister critical thinking - you’re not the parent here. But it’s always part of growing up to realize there are things that you had the wrong idea about- this happens to everybody and it will happen for your sister, too. You cannot prevent her from being affected by harmful viewpoints - but you can be an example of somebody who has grown and changed their mind, corrected a mistake, and found your own way to live. That will do more for her than anything else.