There was only one series of biographies that I know of that included Juliette Lowe, so I think I read the same series as you did. And Thomas Eddison was in the series I am thinking of, as well. The books all started with the childhood of these Americans, right? I don't recall the name of the series, but there should be a ton of them out there as every public and school library I went to as a child in the 1960's had a set, sometimes even two sets.
The ones I recall were usually orange books with black titles and a black logo that included an arch of stars. But sometimes they were other colors (depending on the year the set was published? Sometimes a library's set was mixed colors, not acquired all in the same year?)
I think part of the series title was "Famous Americans," but there was more to it than that. "Heritage" was that in the series name?--Anyway, if you look up Juliette Lowe on Half.com, you will see that there is one book offered with her name. Perhaps you can contact the seller to see if the book is part of the series you are remembering and get the series name from the seller. Or perhaps you can look up the author (Higgins, or Wiggins. I forgot already.) of th JL book and see if she wrote other children's biographies. That could be a clue.
By the way, I did have a chance to revisit those books sometime in adulthood. From my adult perspective I realized how hugely fictionalized they were and how, um, goody-goody and contrived they were. Sort of propaganda-ish. Nonetheless, I loved them as a child, just ate them up.
Hmm, maybe there were two really similar series. I say that because I just was describing above a series focused on Americans, yet I seem to recall that Florence Nightingale was the subject of one book Yet Nightingale was not American.
Let me know if you figure it out, please.