Perguntando em nome de um amigo de um conhecido através de outro site :-)
Buscando um romance de 1970 (ou anterior) envolvendo viagem no tempo e conservação ecológica. Da descrição fornecida:
It involved time travel (unexplained) with a girl, from a future so polluted that there weren't any animals but humans any more, traveling back in time to the mid-20th century and meeting her grandfather or great-grandfather or some such who would grow up to be a famous conservationist. She tries to fit in in the new time and fails.
she finds her way home, and her ancestor gives her some animals to take with her. I specifically remember wolf cubs. (I did not, at that age, wonder what on earth wolves would eat if the future folks ever tried to establish a wild population again. Now... I do wonder. I wonder about lack of genetic diversity, too.)
The copy I read didn't have a dust jacket. I'm pretty sure the cover was light, between white and yellow, and the art was in shades of gray and showed the main character and possibly some animals.