I keep coming across this ◯は◯で, and I’m frustrated that there seems to be no official interpretation in any grammar resource. It was discussed in the first week of the コーヒーが冷めないうちに book club a little. The phrases were similar to your example: 「数は数で「あ。はぁ」と応えただけで、それ以上何も言わなかった」 and later「数も数で核心をついた返事をした」
I’ve also seen it in the phrase: 「まぁその時はその時で」here:
It seems to me like it adds some emphasis and contrast, like “on her part”, “being the way she is”, “being a separate case”. So in your case “because Mia is Mia [rest of sentence]” sounds about right. I’d really like some more definitive answer however.
