Yes, it is wrong to wish it. I understand the frustration you are going through, I have several people in my family who have had past health problems like the ones you describe. There are people in my family I can never forgive for the way they have treated other family members, but I would never wish them harm. I hope you can get some much needed time away from her, and understand as hard as it is for you, it is 10 times harder for her. You have control over your emotions, you can take a step back and try to focus on the good in your life. At this point she clearly can not.
I hope you both find a little peace.