I'm willing to bet, without even reading her reason(s), that she's leaving because the place is just too toxic, or too "far-right" now.

The left wants Twitter to fail so much now. They need it to fail. They cannot stand - they cannot afford - to have a world in which they are not the ones deciding who/what is allowed/not allowed.

The entire rise of the leftism over the last couple years is entirely due to their monopoly on the narrative. Without it, there is zero way they achieve what they have achieved. They need to indoctrinate, and they aren't going to give it up so easily.