Young adult eco-scifi from the 70's

OK, under the heading that nothing is obscure to the SDMB, I’ve been stumped for years as to the title of a book I read in grammar school. It’s a young adult sci-fi novel, along the lines of A Wrinkle In Time. It has a strong ecological bent, and a strong teen female protagonist. Basically, she, for no adequately explored reason, steps through a membranous time window from her time set sometime in the sad, ecologically conscious and regretful (of humanities past ecological failings) future, into the US just before the dust bowl. You can expect her eco-consciousness, strong female attitude, and attitudes on preventing overpopulation do not sit well with the locals. Anyway, the real identifier for this novel is the protagonists name – Paramecia or Para for short, apparently her mother studied them, or something. Google fails me, I can’t filter out the protists and still get useful hits. Can anyone here help?

The Girl Who Slipped Through Time by Paula Hendrich

http://www.rob.com/harriett/solved-g.html
(search for the book title, it’s a long page)

I did a Google search for:
science fiction +Paramecia

as Google was giving me too many results that had a word similar to Paramecia but weren’t the exact right word. Using a plus sign forces it to look for exactly that search term. I found a short reference to a possible title in #2, writework.com, than re-did my search.

D’oh, I suck at Google. Boy is that embarrassing to admit. That is a very useful web page though, for people who remember a bit of the story, not not all of it, (funny what other people thought this particular story was about) so that’s for that.

I was about to suggest H.M. Hoover based on the overall description. But then i’d have been wrong.