Swansong question

I'm looking for a book I read many years ago. It was futuristic, about our sun changing and everyone dying, but younger people change somehow so that they can live under the new sun. Older people can survive if they never go outside. I think there was something to do with DNA and RNA. I've been searching forever it seems. Also, the story kind of surrounds a teen girl who has her face/body surrounded by something akin to a chrysalis........I could have sworn the cover had a picture of her head which was covered by something that looked like a bee hive. It's driving me nuts trying to remember and find it.