Death has to be peaceful after you fight for so long to stay alive. –unknown
Solaris didn’t die in a fire. Being as close to a physical representation of the star that gave the Earth its light would make it difficult to die that way even if she was still, somehow, human.
(How was she still human after several hundred, possibly even a thousand, years of being alive and helping to rule an entire solar system and being part of a very strange monarch/democratic galaxy?)
She didn’t die from wounds inflicted from the battle field.
(And she had seen far more battles than most queens had throughout the history of the Earth, though not put together. She wasn’t quite that old.)
She didn’t die from a broken heart or a shock to the system.
(Her heart had been broken enough times to kill anyone, but she had learned at a young age that allowing such a thing to decide what you were going to do with your life didn’t help anyone.)
Solaris didn’t die of anything that many people would think that a quasi-immortal being who’d helped to rule a vast empire that spanned further than the stars seen on a clear, cold night in the middle of the unoccupied desert on Earth who’d faced numerous wars and invasions of her planet, her solar system and even her entire galaxy. No, she died of something as simple as old age.
Granted that few people ever lived as long as she had who were born during her life time, though there were those who, like her, lived a lot longer than most from her teen years and early adulthood would ever have been able to conceive.
She died happy and peacefully whilst in her own bed, surrounded by her many children, grandchildren, great grandchildren and even great great grandchildren. Her friends and family there as she slipped away between one breath and the next, a smile on her lips and a twinkle still shining in her eyes.