Where does she say that? Doesn't she claim to be (worried about being) triggered by anatomy?

Also, can you quote where JKR says that trans people shouldn't be allowed to transition and that being trans isn't real? That really is very much transphobic--if you want to document her transphobia this should be exhibit #1! You specifically quote her as saying, "I want to be very clear here: I know transition will be a solution for some gender dysphoric people". If you want to make a case that she's transphobic, why quote that but not the other places where she says trans people shouldn't be allowed to transition?

The trans panic defense is specious because there are plenty of other options, like telling your partner that you're not into this and you want to stop. (If they persist, at that point it's sexual assault and then it is legitimate to try to use force to end the assault.) It's a defense against it being premeditated, if that affects sentencing in the jurisdiction at issue. It's not a defense against it being illegal to kill someone.

I agree that people shouldn't get to take important rights away from each other just because someone gets triggered (mental health is also a right, but people must take a great deal of responsibility to handle what they can internally or else society becomes unworkable, and having a working society is a higher-priority right).

However, if there are existing safe spaces (safe psychologically--we'll assume actual violence isn't an issue here) which people like because it reduces the chance they'll be triggered, changing things so the space is less safe for some people so that other people can feel more accepted is...just a straightforward tradeoff between the psychological well-being of two different groups of people. It's not an issue of rights vs. "oh, I'm just triggered, that's on me". If it is an issue of rights, why doesn't it apply to men too: why not just allow men in women's spaces? Why even have gender-specific spaces?

There are lots of ways one could approach this and come up with a consistent viewpoint. But the viewpoint that accepts the desire of trans people to feel comfortable but not the desire of (some) cis women to feel comfortable, or the desire of trans people to not be triggered but not the desire of (some) cis women to not be triggered, is not a consistent one. The first step is either to acknowledge that the concerns are comparable and then argue that one or the other should still get priority; or to very clearly spell out the reason why the concerns are not comparable, and not extend one's conclusions beyond the space where you have argued that they're not comparable.

For instance, "I am literally not allowed to use a bathroom" is not comparable to, "I am irrationally frightened by the thought of some people being in a bathroom I might use". But I don't think JKR is clearly documented as saying that. (Generally, it's well accepted that basic physical needs trump presumed psychological safety, and saying otherwise in the case of trans people would legitimately be an instance of transphobia.)