Hi, and welcome!
I am currently using R& S 6 with my 7th grader, and I would guess that would be a good place to start your 7th grader. You could do the first half for 7th and the second half for 8th. Rod and Staff moves very fast from grades 4 through 8, and the grade 7 and 8 books are totally high school worthy. My 7th grader is doing really well with level 6. Or, yuo could do all of level 5 in grade 7 and all of level 6 in grade 8. Either way, she would be on track. Also, Carrie recommends using the Rod and Staff English in a very different way than written. What we do, based on her recommendations, is we do orally the 5 or so review questions at the bottom of each lesson in the teacher guide. I do not do the "presenting the lesson" section, but rather have my daughter read the lesson herself from the student text. Then we do the "class practice" or "oral drill" orally or on the white board, whichever makes more sense (if it's diagramming it goes on the board). Then I choose about 1/4 of the "written exercises" for her to do written in her notebook, and the rest we do orally or on the whiteboard. If she demonstrates that she has understood the lesson well after only half of the exercises, we call it a day. This all takes 30 minutes or less, and she is retaining very well! Rod and Staff also includes the application of grammar to writing, and at this level includes outlining and writing paragraphs and essays.
About science, even from down in the lower grades, the students are taught the scientific method and writing lab reports. They are simpler, of course, in the younger grades, but increase in complexity each subsequent guide. By Rev to Rev, the student will be writing lab reports, writing narrations, and making notebooking pages with science, as well as reading living books and building projects. I encourage you to look here for more info on the science in Rev to Rev
http://www.heartofdakota.com/revival-to ... inventions and here for a sample of the first week of lessons
http://www.heartofdakota.com/pdf/reviva ... e-week.pdf There is so much more than meets the eye in Heart of Dakota's progression of skills in science, but yes, it is flexible enough for you to substitute if you prefer something else.
I would encourage you to give DITHOR a try too. It has a student level 6/7/8, which would be perfect for your daughter. You would use either the Sample Book Ideas List to purchase or borrow from your local library age-appropriate books to use for each of the 9 genres covered in DITHOR, or a book package (I believe Heart of Dakota will soon offer higher-level book packages for DITHOR), or just choose your own. It is an excellent literature program but goes beyond just literature analysis. It includes Christian character study, Biblical connections, and book projects as well.