We're going on Friday to see DH's sister. Her cancer had affected her kidneys back when her cancer was discovered and she's been on dialysis ever since. She has stopped that starting this week so I don't know between the cancer and not having dialysis how long she will live. DH's brother that visited her over the weekend said that she throws up a lot of what she eats and has to watch her fluid intake. She's a nurse so she understands what she is going through and the process but that doesn't make it any easier. She has all the drugs and morphine she needs to help with the pain. I'm praying for a peaceful passing. DH's oldest brother didn't have one, I pray that she does.
I am so sorry to read this. I had to reply because I went through this with my dad. My dad was on dialysis first (end-stage renal disease,) and was on it for 6.5 years by the time he died. He developed colon cancer, and had had it for a little more than 3 years, but they determined the kidney disease was the primary cause of death (which does make sense - at his age, 6 years is average life expectancy following renal failure.)
In my dad's case, he could no longer stand in order to get to dialysis at the end of his life. He usually went Monday, Wednesday, Friday, and the week before he made Wednesday but then missed Friday, then missed Monday. Then Wednesday, he technically missed again because he went to the hospital, and died that night. So, about a week. He threw up everything he ate starting that Friday (and ate very little in general,) and the day he died he threw up "coffee grounds" (black and chunky) two or three times.
I would say my dad's death was peaceful, though very abrupt. He just quietly stopped breathing and that was that. One second there, the next second "__________________" on the monitors. There was a panicked interim, where they resuscitated him because he didn't have a DNR - if your DH's sister is a nurse and is aware her life is at its end, she probably has one, which will avoid what we went through. I hope that (barring the resuscitation part, which truly was the most garish part of his death) your DH's sister has a peaceful passing like my dad did. Peace be with you.