You could just go ask what the previous books used were, or look at what some gifted schools use for texts in 7th, 8th grade science. I'm not sure how fun/useful such a text is, especially if disconnected from the course, but nothing wrong with trying. Just because something only MIGHT work, is not a reason not to do it.
My 7th and 8th grade G/T experience was a course in "environmental science" that was descriptive ecology. Nothing wrong with it and fun and fascinating. Then a course in "introductory physical science", which was baby chem/physics with an emphasis on measurements and units (and some fun experiments like making fudge...and methanol). I don't really recall the texts used and the classes really were more instructor led.
Two books that many great physicists say inspired them as children are Microbe Hunters and Men of Mathematics. Both are early 20th century but still resonate today. (MoM has one woman in it, also, if that is a concern.)
I would also suggest the books by Richard Feynman: Surely You're Joking, Mr. Feynman and What Do You Care What Other People Think. Very readable and fun. The last half of the latter book is about the first Space Shuttle crash investigation and is eerie in how prescient it was of the second crash.
You could also sign up for Things of Science. They mail you a little blue box with science experiments in them. I tried doing it in 5th grade, at my dad's urging, but was too young for it (was too hard). But smart middle schooler lacking textbook would be perfect customer. [If that doesn't exist any more, consider to buy her some other kits.]