I went through this, OP, with both of my parents. They'd jointly decided to donate their bodies. When my father died over 30 years ago, my mother made the arrangements with a local, major, teaching hospital. She declined receiving his ashes back.
When my mother was dying, about 6 years ago, she reminded me of her wish to donate her body. Indeed, she wanted me to call the medical examiner (the official where she was living to coordinate donation) just a couple of weeks before she died. I insisted on waiting until she was taking her nap, but as soon as she awakened, she asked if I'd made the call and what the results were. I told her I had, and that I knew what to do. She also made a specific request that she did not want her ashes returned - in her words, she didn't want to spend any time on a mantel.
Spending the last couple of months with my mother as she was dying (and she knew, and accepted it) was perhaps one of the most profound times of my life. As sad as I was to have lost her, the donation experience gave me (and continues to give me) a smile. After she died - at home, in her bed - I called the medical examiner. The medical examiner's office proceeded to ask me a series of questions - had she had any infection diseases, what was the cause of death, etc. - then she asked: "Was she straight?". I paused. I answered: "I think so." The questioner pushed: "You don't know if she was straight?" I told her mother was 89, married for many years, and had children, and I had no reason to believe she wasn't straight. At that point, the questioner told me that wasn't what she meant. By "straight", she meant physically not atrophied, bent or curled.
At that point I understood. Most people die in hospitals or other medical facilities, and most times the medical examiner is talking with a nurse or other medical professional who would have understood the question in context. But today, I still smile at that conversation - and I suspect the person on the other end does likewise.
Our family has never regretted the decision. She had a wonderful memorial service at her church - standing room only - followed by a lunch catered by the group she told me to call to cater it. We needed no casket to celebrate her life.
And at the end of the day, it was absolutely her decision.