So, madeinuk, I was re-reading this thread and feel like your original question got a bit lost.

Do you have more specifics on what you’re looking for? You asked about a class in the title, are you asking for suggestions about a class explicitly for study skills? You mentioned perfectionism and despondency, maybe more details would help others to understand what you are looking for. Part of the problem may be as others have noted, “studying” is kind of a broad term and has many different interpretations.

I’m sorry but we don’t have any help as far as classes go, although I do know others who have taken classes of this sort, everything from speed-reading to organizational/time management strategies to specific test prep classes, though I’m not clear if that’s what you’re asking about.

As far as studying academically goes, as you noted in your question, our kids didn’t seem to do a lot of that, though I think it really depends on what type of class/subject you’re talking about. So many classes in HS were much more about written work or presentations, I feel like there were not many typical “tests”.
For things like math and science, the teachers did a lot of scaffolding (too much, in my opinion) where there was often a review packet or similar materials that were assigned, so everyone had to do it- this was more than enough. If that’s not happening, I think I would have her look for problems to work, either in the textbook or online, or in a review book, that correspond with the unit/material. For things like history, the AP classes did have a lot of multiple choice “quizzes”- these my kids did study for, as the level of detail and volume of material was crazy. They had to take notes on the readings for class, so these were reviewed (sometimes re-writing/organizing them can help and is enough to commit them to memory). They also used material from review books specific to the subject where they could basically do practice questions or tests. I think this is a good strategy for standardized tests, too. Our library offers free practice tests for SAT and ACT testing a couple times a year, given under the same conditions as a real test, though you could certainly replicate much of this at home. I have also heard that the Kahn academy SAT materials are good, though no direct experience.

If the issue is perfectionism, we definitely have experience with that, as I’m sure many others here do. I can’t say that we managed it that effectively, to be honest. The most helpful things we did do involved finding opportunities outside of the regular classroom where learning (and sometimes studying) happened, so that it was kind of divorced from grades, the competitive atmosphere of peers, etc. We made sure to emphasize the learning and not the grade, and generally didn’t put much stock in things like GPA, though that is hard to avoid if your school values it (ours is thankfully moving away from this trend, and reports only which decile kids fall into). Studying music helped for DD, though she had to wait until high school and wider opportunities were presented before she was able to stretch herself and really need/want to work hard at it. I’ve mentioned the science olympiad team before- again, this was an opportunity where motivations were related to a group effort and common good, very important for my socially-focused DD. I think athletics, even volunteering, or other challenging opportunities where kids are out of their comfort zone and want to/have to push themselves to improve can be a huge help. You want to find a way to tap into their intrinsic motivation, though that can be hard to find, I know.

Hope some of this ramble is helpful, and that your DD finds what works for her.