>>149422894
>its the same thing.
No, it's not. Imagine the exact same situation, but instead, it's a cis black girl and she call her a racial slur.

>>149422903
>There was no in-universe indication that Mary was aware that Carla was trans at the time.
Her remark there is all the information you need to establish that she know. You don't need more than that for the story to make sense.

I do'nt see how the readers only learning at this point that Mary know Carla is trans is relevant anyway.