Many similar good pieces of advice in sibling comments, but I'll add my agreement to this one.
From the subject line, I came in all fired up to start with "just quit; it's the greatest market for SWEs that the world has ever seen". After reading some of the details, I'm inclined to think "eh, it's some poor leadership being shown, but it doesn't sound irretrievably broken anywhere yet."
Start with your direct manager and setup an hour long 1:1. Let her know that you have some mixture of confusion and a small amount of concern, but that you're focused on understanding the feedback and, where appropriate, using it to improve. I think it's terrible form for your manager to bail on the 1:1:1 meeting and, if she had to, your skip-level manager should have rescheduled it. It's not just development for you, but it's development for her and while you should be having quarterly or so skip-level meetings with them, you should never be in a position as a fairly fresh grad to have your project work reviewed in a setup like this one. Poor leadership technique (IMO), but it's not evidence of anything toxic if they're open to "yeah, that sucked; we won't do that again".
I'm often in the role of wondering "why the hell is this project taking so long?!" and simultaneously realistic that there are generally very good reasons for it. (How many software projects in the history of world took wildly less time than originally contemplated?) Two years from now, I expect you to have developed a clear sense of how to explain those justified delays in a way that's convincing and non-defensive, but it's pretty damn unfair to expect you to be able to do that now, especially if you're a summer 2021 grad. You're spending all your time busting tail to just get the damn thing to work and someone's chirping about a second-order effect ("sure, it works, but why'd it take so long?" is just not a question that you're well-positioned to evaluate yet).
I think your overall approach and attitude here is going to serve you well in your career and dive into this one head-on and with curiosity with your direct manager. You've always got the great SWE market to fall back on, but this one seems like staying and fixing is a better plan.