You may enrich her desire to read by continuing to converse with her, playing with her, reading to her and telling her stories. These are but a few of the activities that you can engage her in that are appropriate for her age. Use our site's search function to type in "learning to read" -- we have loads of great tips and resources for you that will benefit your sister. You may also be able to use the information in Stages of Reading Development, a book by Professor Jeanne Chall.
You are a kind and loving sister and she is blessed to have you. Thanks for writing and for understanding what is appropriate for your sister at this time.