How to handle negative people?

I carpool with a very negative close relative. I generally have a very positive attitude on life, I have practiced meditation and been very into Buddhist philosophy. I have found my self straying from this positive path and feeling depressed and down after riding with this person for so long. It is a 45 minute drive and it is just everyone elses fault her life is so crappy, but she does absolutely nothing to try and change the events in her life. It is like she truly enjoys being pitied. For a while I went out of my way to help her thinking it was just bad luck on her part, but then she started taking advantage of my generosity. I have no idea what to do, I have to be around this person but I don't know how to handle the negativity and get back on my positive path. I have tried talking with her but she just goes quiet and acts like its nothing. Please give me any suggestions on how to handle this?