I am responsible for my sister

My sister is a fresh at University from this April, and has a lot of classes and of course assignments. Those are almost English assignments, but she is not good at English that she is now really busy just doing them. And sometimes she has to stay up late, and I have to help her as a big brother. Those are really easy to me of course, so I do them in a very short time. But I realized that recently that kind my assistance continued too much, I helped on every single assignments, she does not do them on her own. And I do them quickly, maybe she is using me.
I am like function(). if she call me as a function with a assignment as a argument, then I return finished assignment. It is like this, Finished_Assignment Yusuke(UnFinished_assignment);
In the computer science, that is called information hiding, users don't have to care what's going on inside function, users just know how to use it. But it is ENGLISH!!!! She's got to be able to use it fluently. I think she can't do them because her base of English is not accomplished yet that should have done by she finished high-school, the reality is harsh. In my experience, I first had a strong ground in grammar and vocabulary, and then I did Listening very hard, after these, I realized that I can write and speak to a certain extent, so now I have to sharpen these by practicing writing a lot and speaking out. I can help my sister, but I don't know whether I am bothering her from improving, does she have to do them by her own or not? I know at least that I am responsible for her. Part of her life is up to me. I think I will help her if she finishes by her own. I will revise and edit.