Bill Hicks explained this so long ago: Fevered Egos.
Seriously, lead writer throws lead designer under the bus because of... an interview. (somewhere).
Like, how much of a narcissist do you have to be to go off on a Twitter rant over... what? Exactly?
What sort of "professional" shit-talks their co-workers on social media?
The giveaway for me is the "undermining" thing. I literally cannot imagine a scenario where a lead writer would not be below a lead designer in the hierarchy of dev. She's not the fucking game director. The way she's putting it across is that this guy somehow "sabotaged" her vision, when even if the guy is a total dickhead, him disagreeing with her on creative matters is perfectly legit.
If there was any sort of personal animus between them, the same thing applies. Like any other job, some people you get along with better than others. Some people are more on your wavelength than others...
What she's saying is horrifically unprofessional. Beyond the pretty unpleasant intent of trying a colleague in the court of public opinion, its just so arrogant and presumptuous for somebody in her position on the team.
What's especially galling is the twist of the knife in the "this is the reality of being a woman in this industry". Not only does that imply misogyny, but the sheer fucking hubris of thinking that what's happened to her hasn't happened in the past to other people of both sexes!
Fevered Ego.