I am sorry to hear that she is sick. I know just how you feel. When I D XWH#1, I had 2 ExMIL's and 2 ExFIL's (they had remarried), so I felt I lost so much. Both my parents were deceased already, so they were my only family. I did go see one set of his parents a couple of years ago. I truely loved my ExFIL and he never did anything to hurt me and he was dying. I also went to his funeral last year. My other ExMIL and ExFIL have also both died in the last few years but I wasn't invited to the funeral so I didn't attend.
So now I am down to one ExMIL, who just fell a few weeks ago and broke her leg. Her sister called me from the ER before her surgery, but I didn't go to the hospital. They have since put her into a nursing home and I have called and spoke with her and will probably go see her this week.I knew one set of my ex's parents did not care to see me, so I never went out of my way to see them. I was always respectful and cordial if they showed up at any of my kids activities, but I did not visit them and they never visited me. I feel they are the ones that missed out by taking sides during the D.
I also have a new MIL and FIL by WH#2. After DDay#1 they showed me that if I D'd their son that they would be OK with me seeing them. It was awkward for a little while, but it got better. After DDay#2 they told me they wouldn't blame me if I did D him. It is a fine line to walk for sure.
It is hard to know what to do after you D in regards to the Ex's family. I think you just have to play it by ear and do what makes you feel good in your heart. Maybe call her and see what she says and see if she would like a visit from you. That is how I handled seeing my beloved exFIL before he died. I just made sure my ex wasn't there or wouldn't possibly be there when I showed up and it worked out fine. After all, you didn't D his family, you D him. (((HUGS)))