Don’t waive your right to see the letter.
Your GC may just be lazy and want to avoid the extra work of preparing an ED app to a private school. So the letter might be proforma, but not insulting. I know that in California where I live, the public universities don’t require recommendation letters, so any private college that uses the common app is extra work compared to the vast majority of the students who just apply in-state.
But if the g.c. knows you will be able to see the letter, she might be a lot more careful in how she phrases things.
Your grades and class rank are what they are, it can’t be changed one way or another by what a g.c.says…
I agree with others that Dartmouth is a reach for just about everyone, but you are competetive for admission there You can’t get in if you don’t apply – so if that is your dream school, go for it. But be careful of ED if you need financial aid – especially if your parents’ finances are complicated in any way (for example, self-employment or other income from sources other than W2 wages).
If you opt for RD, you do need matches and safeties, but don’t be afraid to throw in a couple of more reaches as well. You can tell your g.c. that you appreciate her advice but that this is the only chance you will get to try to get into top schools and you want to at least be able to put your best effort into getting into a top college.
Assuming you are female, don’t be afraid to apply to women’s college as well – there is an admissions advantage that comes from eliminating half of the potential applicant pool.
Your EC’s are great – you are going to be able to present yourself well on an application.
Humanities majors are fine.
In life there will always be authority figures who are jerks and try to undermine you. Now it’s a high school g.c., someday it will be a manager you are stuck working under at a job. It sucks, but it’s what it is. Don’t let people like that get you down, and plug right ahead toward your goals.
Go see Lady Bird. You are not alone. In the movie, her g.c. laughs at her. (And remember that Lady Bird is a semi-autobiographical movie made by a young woman who attended Barnard and majored in philosophy and now is a famous actress & movie director - so not a total movie fantasy about getting into a dream college.)