Rather than feel pity, she's heartened: Shakespeare's words "Fear no more the heat of the sun" (from Cymbeline), return to her. These words connect Clarissa and Septimus (he had remembered them earlier in the novel), and suggest an end to fearing death, something that has haunted Clarissa throughout the story.
Answer: Even with the warm weather, there was still a vestige of snow on the ground. Vestige is a trace of something that is disappearing or no longer exists.
