Adding a commit to a colleague PR

Hi everyone, I recently did a mistake of adding a commit to a colleague PR and I'd like to know how big of deal would be that for you. One day a colleague from the frontend team comes to me asking to review and merge a PR from a backend colleague. I reviewer the PR and replied that cannot approve and merge because there where things I did non like and a security issue. We both discuss changes and then I added a commit to the PR waiting for the day after to come back the original author of the PR to show her the changes made and discuss the solution agreed with the frontend. But, when she got back (the day after) got mad at me and reported it to the manager telling him that I imposed my point of view even though I immediately apologized to her and told that she could delete my commit if the solution was not good for her. In order to learn, what is the PR netiquette? Adding a commit to a PR when you are not the author is really bad? Thanks in advance 😀