What real benefit to a student wanting to join the Navy is JR ROTC in school?

The only advantage staying in would be that if she enlists and has done 3 years of JROTC, she will be advanced in rank so more money. JROTC however can actually be detrimental to junior enlisted personnel. They get trained in high school and think they know it all when they get to basic, and they have to be unlearned at that point to relearn the real military way.

I would think the primary advantage is that it gives the student a good look at what they will be getting into when they join the service. I'm guessing that JR ROTC is in high school and that the school is run along the lines of a military institution. If the student can't handle military obedience and fitness requirements in school, then they should not consider it for a career.

One real benefit would be more money. If the program is still the same as when I was in high school, you can join as an E-3 if you complete 3 years of JROTC, which can be a considerable boost in initial pay.

Well I'm in Air Force JROTC as a freshmen right now and we're learning about leadership, sciences, and we are doing physical training. I don't think that you should pull her out of the class. You should at least consider letting her stay as a cadet until the end of the school year.