Being Accused of using AI when I didn't

Kinda a rant but I really need to get this out.I have seen this kind of posts a lot but didn't know it could happen to me. The assignment is for my project management class and it's a very easy assignment. We just need to write a business memo to stakeholders to update the status of the proejct and challenges we face. Pretty easy right? I didn't even think about having to use chatgpt or Google for it. But I ended up getting a 0 for it and the professor said I have a high percentage of AI used in this assignment. She did give me a chance to rewrite but it's just so frustrating. My mistake is that I wrote the assignment in my local Word file so I couldn't provide her a version history of my edits like in Google Doc.

What makes it more infuriating is that in class she mentioned this issue of using AI for homework and she said ' we all use AI for information but please do your own writing. And if you get caught, don't have say something like oh professor I didn't use AI. Just say oh I'm sorry I wouldn't do it again and be careful next time'. It's so upsetting that she just assumeed I'm lying and assume everyone uses AI for everything. I feel like submitting an essay is not about research and writing anymore, it's about how not to get caught by the schools precious AI Detection tool.