70s (or earlier) time travel SF conservationism

ETA: They found it! It was The Girl Who Slipped Through Time by Paula Hendrich.

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Asking on behalf of a friend:

I don't remember the title or author of my first SF book, but I remember the plot. 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. Eventually, 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.

Any ideas would be greatly appreciated, thank you! ^_^

Although it has a male protagonist, Larry Niven's Flight of the Horse short-story collection (1973) has a similar time-traveling conservationist theme. One story also features a singular adult wolf (kinda) brought forward through time (sort of) -- no puppies though, as far as I recall.

Thank you for the suggestion! I've passed it on, but unfortunately that wasn't it. It did spark a few new details on the story, so hopefully those will help someone figure it out. ^_^

They said that it was definitely a full-length novel and was aimed at 3rd-6th grader in the US. They also ruled out Andre Norton's work as potentials.

They found it! It was The Girl Who Slipped Through Time by Paula Hendrich.

So glad you were successful! Thanks for coming back and letting us know.