I am specifically talking about when it applies to other people. For example, you are talking to her and someone else interrupts. If she would say something sharp to embarrass that person, that is a chance to say, “that was a bit harsh”, or maybe even, “I think you are a bit harsh on that person”. This is very different than saying it when it applies to you. When it is about someone else, it is in a sense you with her against the other person. You are telling her as a team mate rather than an opponent.
But definitely, what Aries mentioned goes first. I an saying this in case you actually do want to make inroads.