I have moved your post to the "Teaching English" section as it is more appropriate.
You said "Her English is not good". I take it from that that she does speak some English. If so, use that as your basis. Have simple conversations with her which include much of the vocabulary she already understands but add in new words here and there. Help her to get used to hearing English by playing English-speaking radio stations in the house as often as possible. You don't need to sit and listen to it, just be surrounded by it whenever you can. You can teach her individual words by simply pointing at things in your house and telling her the English word for them, getting her to repeat the word, then put it into a simple relevant sentence. Let's say she doesn't know the word "dress" (noun). Find a blue dress she owns, and get her to say "My dress is blue". If she already knows "My", "is" and "blue", then she has now learnt a new word and she will remember it more easily because it refers to something she actually owns.
Your profile says you are an English teacher. How would you teach a beginner student?