Immortality thanks to nanotechnology

Trying to find a short story. I first read it approx 5 years ago. It was part of a short story collection from various authors. I can only guess at the original published date, but the paperback I read it in was in good condition and seemed fairly new. Written in English.

Story focused around a woman, who for some reason had been injected /infected with a form of nanotechnology (I think that was the term used). These nanobots initially repaired any injury or damage the woman received. However as the years pass the nanobots have repaired so much of the woman that little or no flesh or blood exists, even replacing elements of the brain. The woman is still lucid and self aware.

The consequence of the repairing is the woman is now unable to die, and immortal (I think). As the years pass by she witnesses the end of the earth and the death of the sun in a supernova.

This is as far into the story as I can remember. If an answer was to include where I can read the story again that'd be great.

I'm familiar with many of the works of the classic sci fi authors, and I believe if I'd heard of the author before I would have remembered their name, and therefore found the story myself.

Thanks