The reason people are saying that Dana Terrace is in the TWERF pipeline is mainly due to 4 reasons.
She reacted very differently to the transfem headcanon than other headcananons, such as ships, sexualities and transmasc interpretations.
Despite being praised as a "queer creator" she has no transfem characters, despite having multiple transmasc characters in her earlier works. (She does have a joke character voiced by a transphobe, which some people have claimed is meant to be seen as transfem, but if that is the case then she is basically just doing a new version of the Hays Code.
She has now deleted her only tweet which could be seen as having any support for transfems, where she called Disney gutless for pulling a transfem storyline.
According to data from clear sky, the only people she has blocked during this ordeal has been transfems, most of which have been pretty polite. One of the responses was literally just "as a trans woman, this disappoints me and I won't be watching the show", slightly paraphrasing here, you can check it out in more depth om clearsky. If she had been blocking more liberally I would not see this as a red flag, but as of now the criticism from TME people is still up and much of that is less polite. Trans women tend to be walking on glass shards when it comes to criticising someone like this, but TME people can be a bit harsher and many allies often are, as they recognize their privilege and use it to speak up. The point is, these allies have not been blocked, despite having harsher tones than their transfem counterparts.
In conclusion, each of these points on their own does not really support the interpratation that she is in the TWERF pipeline, but all four together does paint a worrying picture. I think that it is unlikely that she does go full mask off, but it is worth mentioning that people were saying similiar stuff about JK Rowling in 2016, despite many TME trans people insisting that her TERF behaviour started in 2019 or 2020, depending on what each person sees as the breaking point. If someone is "only" transmisogynist a lot of TME people refuse to pick up the signs, which is what happened with JK Rowling. Considering how that played out and how TME trans people called transfems "hysterical" and "overreacting" back then I don't think you should throw around those accusations too haphazardly.
So, here's the thing. I'm not trans - I'm not transfem, transmasc, non-binary, agender, or any other gender identity other than cis male. I can't prepend to understand how trans people feel when they see something or someone who they see as representing them torn away from them even if it was done in a polite and carrying way. It saddens me when any LGBTQ+ person loses something that comforts them, validates their identity, or makes them feel seen.
That said, you have to admit that you're viewing all of this through a very narrow and biased lens. For instance, why assume that Dana's clarification of Frankie's gender is anti-transfem and not say anti-transmasc? Frankie, if anything, is telegraphed to be more transmasc than transfem - and while that's an opinion of mine, I think it's a well founded one. She doesn't even mention specifics here, even the person asking only askes "is Frankie trans," so why make these assumptions?
So consider that you're going into this situation with a bias, and when you're piecing together other bits of info, that bias will still influence how you interpret that info and color the picture you're building of Dana. Confirmation bias is a powerful and dangerous phenomenon - just look at the Tylenol causes autism or anti-vaxxer scares going on right now: aside from the political nonsense behind these things, confirmation bias is the culprit behind the vast majority of peoples' belief these unscientific, unfounded ideas are true.
So I'm not going to try to refute each of your points, I don't think that would be productive. Though there is one thing I'd like to address specifically: making any comparison, no matter how small, between Dana Terrace and JK Rowling is absolutely uncalled for. JK Rowling's track record of bigoted and hatful ideology was well established before she became the grand wizard of the TERFs. Dana Terrace, on the other hand, has been an consistent and vocal supporter of LGBTQ+ people as evidenced by her work and her public statements and actions even to her own professional detriment. I understand fearing that someone you like and respect could turn out to be a rancid person like what happened with JK Rowling, but in her case the indicators of her rancid way of thinking were all clearly evident well before she was publicly known to be a transphobe. Simply put, given what we know of Dana Terrace, any suspicion of this kind of hatred in her heart is the result of paranoia. It's unhealthy, and even though it's something that I can't blame a person for feeling, I can take issue with people pushing their paranoid beliefs in the public sphere to the detriment of others. If an African-American man cites the Tuskegee Syphilis Study a the reason to be skeptical of government related medical efforts like vaccinations, I can understand why he feels that way given what happen to those men and empathize with him, but I can still feel compelled to speak out against paranoid anti-vaxxer rhetoric.
I'd like to end this off with my original sentiment, please as a fandom for the Knights of Guinevere, please let's give Dana the grace she has earned and deserves and not repeat the mistakes of other fandoms and turn on each other, filling the space with toxicity and bile.
