How do I cope with caring for a mother that is going to outlive me because of the stress she puts on me?

First let me say my relationship w/my mom was good until I had a daughter and realized how badly she's always treated me because I would never do or say things to my daughter that previously had seemed normal to me. We had little contact because I could never do enough and that was so stressful to me I decided not to do anything. Then 2 years ago, she had an anurysm burst and we stepped in and helped my step dad (then 80) while my mom was in the hospital. She was released after 7 weeks (5 in intensive care and 2 in rehab) 2 weeks later I had a massive stroke and had to learn to retype/rewrite and walk. Now my step dad has been dead for a year and my 86 year old narcissic mother is living with my husband and I.
Needless to say, we're under more stress than before my stroke. We have turned our lives upside down for her but she doesn't appreciate it but expects it. I recently overheard her telling a friend on the phone she doesn't deserve to be treated like this- and has all her friends convinced she is being treated badly.
She is going to outlive us both because the world revolves around her and she could careless about the strain she creates with her attitude and inconsiderate ways. We've had numberous discussions w/her and she may improve for a day or two but goes back to her thoughtless words and deeds not to mention the mess she leaves in her wake that she expects us to clean up. We can't afford a nursing home and being an only child, the caregiving falls on me. I have to keep a very close watch on my BP and 3 or 4 times a week take clonidine to bring it down from stroke levels. My husband tries to buffer the situation but his health is bad too which is very stressful not only for him but me because I worry about him. I'm the only one working and feel (esp today) that everything is just toooooo much. We are open to ANY suggestions how to cope!