Setting boundaries would be what you may want to continue doing. She is trying to make you a codependent in her life (and is going to continue to take advantage of you if you allow her)
She should not be able to turn others away form you (that must be their own choice) and you will want to find out what is she telling them and let them know your side of the story.
If there are others who agree with your approach, include them in your intervention towards this relative (have them take up your side) You just have to say enough is enough at some point (otherwise this will continue to go on)
some book suggestions
Too Nice for Your Own Good : How to Stop Making 9 Self-Sabotaging Mistakes by Duke Robinson (Paperback - Nov. 1, 2000)
How to Say No Without Feeling Guilty: And Say Yes to More Time, and What Matters Most to You by Patti Breitman and Connie Hatch (Paperback - Feb. 13, 2001)
She is playing mind games (being passive aggressive) The only other book that comes to mind is
Toxic People: 10 Ways Of Dealing With People Who Make Your Life Miserable by Lillian Glass (Paperback - Feb. 15, 1997)