That could only work if her words were passed without her being present. But she was present and heard what maid said since she next to her. Plus would servant disrespect her mistress like that by saying totally opposite things than she was being told to? I would say that it's inconsistent writing.
Except as I already pointed out, the frames with the maid speaking to him only had the maids head. We do not know if she was still next to her, or whether she approached the gate to pass on the messages (manga don't need to represent real time, or show every action a person does). Every time
anyone near the gate (not just MC) spoke towards her at that distance, their font shifted (although
likely more emotion than the volume), and 60% of the maids speech did not have that applied to it, only when describing killing him did her font change. While it would be rude for the maid to change the message, we do have the servants confirming they themselves will never forgive him, etc, and it would indeed be for her own good for the original body owner to be kept away from her.
Basically, unless a character re-iterates and confirms what happened, there isn't actually enough evidence to prove whether it was the real message and whether it was spoken in hearable distance. If they were thinking ahead, they honestly could have purposely done it subjectively like this, that if the maid could speak (and not yell) next to her at that distance why couldn't she say it herself, etc. that purposely not letting us hear her whispers to the maid and only showing the maids head to not confirm her location when passing messages.