My aunt was one of those who chose not to slow down, even although she knew she had a dicey heart valve.
My father, her BIL not her brother, but a doctor, asked her if she realised she might be running the risk of shortening her life.
She replied that none of us live for ever, and that she personally had no desire to spend the last months or years of her life in a nursing home, but would rather die in her tracks.
This is, I think, a reasonable point of view, and most if not all of us will be faced with considering how we want to end our lives, sooner or later.
Try not to let your friend's decision worry you, even although you seem to have made the opposite choice. Her life - her death- her choice.