What is your opinion about a student taking the GED Test before moving onto college. She will still be learning from home until she is finished with her senior studies and will be preparing for college and the SAT in the mean time. I thought however, it might be helpful for her to pass the GED first since she is still behind in a few subjects.
A GED is usually not necessary. Most colleges do not require them, and I don't usually recommend that students take that test. If the student scores well on the SAT (500 or more in each section) then there is no benefit to the college for having a GED.
It would be a good idea to go over your high school plan, though, and create a transcript. When you have done that you will know if she is TRULY behind, or if you just FEEL like she is behind. It can be difficult to see the forest through the trees sometimes.