A lot of Mirandy fic* (and okay femslesh fic of a certain generation) has a lot of......"Woaw I've Never Even Considered A Woman But She's So So So I Must!" there's an element of "girl-on-girl-first-time-both-het-kissing" that can sometimes show up, and while of course this can appear in slash as well, it's much less prevalent these days.
All that to say, where the HECK is the 80k comphet lesbian two kids three divorces Miranda Priestly character study. This would be my heated rivalry. Do I need to write it myself?
People can write whatever they want, but speaking as someone who has read a lot of Mirandy fic over the years, there seems to be a lot of "well homophobia doesn't exist in NYC in 2006 and there's no need to give either of them a romantic history with other women and exploring developing queerness is for DUMMIES let's play house**" and like. trust me. I've really really enjoyed some of those fics, and I've come across the type in other places before. However other fandoms usually have a balance, with more nuanced approaches when it comes to sexuality and past romantic history, and with Mirandy/TDWP I just haven't seen that.
(I'm not kidding about and interpretation of Miranda as a lesbian. I'm not going to make any promises about what I will or won't write until the new film comes out but it is On My Mind.)
*If you think I'm vagueing one specific fic, I'm really not
**I'm so deadly serious there are a lot of these. Yes some of them are derivative but it's basically a subgenre of the fandom I promise this isn't aimed at any one writer or even a group of writers.