Is writing "white, female, upper-class" as bad as I think it is?

Yes, some admissions readers may not think of the OP’s accomplishments as impressive as similar accomplishments from an applicant from a disadvantaged background.

On the other hand, being blatant about it in the counselor’s report may not make that much difference, since all of that tends to be fairly obvious from the rest of the application.

There are some very upper income families who are definitely NOT upper class (big-time drug dealers?). Upper class and upper income are 2 different things. I don’t think using the “class” term is a good idea on US apps. It does sound very pretentious. In any case, I agree with others that it is a waste of space to include demographics in a Counselor’s letter.

Um… Kenyon? And all the LACs with a 40/60 M/F split? All of them are harder for a white female to gain access to. I certainly agree that the schools will figure it out anyway… but if I were an admissions officer, I would think it gets the recommendation off to a bad start – kind of tin-eared to the purpose of the recommendation. And brings the writer’s judgement into question. But it sounds like you are stuck with it.

It makes me wonder if she is making “unforced errors” in the rest of the document, though. I suspect your apps might benefit by a review by a paid college counselor… and I almost never recommend that.

When selecting sleeping berths, for example, traditionally there was an upper a middle and a lower.

You can only correctly call upper income people “upper class” if you also call “lower income” people “lower class.” My concern is that the use of the former is likely to bring to mind the latter which may, in the Adcom’s mind, cast a negative light on the applicant. I don’t believe that will help her.

No, but that’s just because everyone wants to refer to themselves as “middle class” or at most “upper middle class”

Unless she wasn’t supposed to mention SES in that section, I don’t see the issue - unless you think she’s delusional about your family’s wealth (which odds are, she has a better grasp than you do).

Better to be privileged and acknowledge that one is privileged than to be privileged and try to pretend that one isn’t.

OP, it will not help you and it might hurt you (my first reaction was 'does the mother NOT want the OP to go away to college- what is the rest of the rec like?!). The question for you is whether removing a possible negative from your app is worth the possibility that your mother will “kill” you. Imo, a college applicant should be able to say "actually, that can come across the wrong way- well off white girls are ORM at many of the schools that I am applying to, so could you change that to (X). But: I don’t know you, your mother or your relationship.