Take the original message that she sent you with the plagiarized material to the professor. "Professor, I realized that Darwin plagiarized much of the material she sent me for this previous report. I didn't actually use very much of her contribution when I submitted the final project, so hopefully none of the plagiarism ended up in our group's report."
I wasn't really worried about that part because she gave me enough to work with and had just sort of copied and pasted in a couple of paragraphs randomly, but I do have all her work archived in my email. Actually it was just two short paragraphs that she randomly inserted - my guess is that she copied them over to keep them handy for when she worked (so she didn't have to open her references every time) and forgot to delete them. But still, if I had blindly added her section, the results would not have been good. I hadn't considered emailing about this, just the personal attack/passive aggressive stuff from today, but both together make her sound worse, so I'll keep that in mind if I need to send that email.
Personally, I wouldn't worry about making her look bad or not. I'd worry about accidentally including something from a known plagiarist. Do you have any more group projects this semester? What if she gets so disorganized that you run out of time to double-check her thoroughly enough?
I would consider it the team leader's duty to push back on plagiarism in a group project, either by calling out the perpetrator and sending it back to be re-done, or by reporting it. That's not "poor work." That's a serious breach of academic integrity. Does your school have an honor code? At my college (back when dinosaurs roamed the earth), knowingly protecting someone from the consequences of a violation, was itself a violation of the code.