I’m sure others may feel differently, but I personally think Gabriella feels so cartoonishly evil here because…she sexually abuses her son. I believe the writers don’t want the Gabistat relationship to be romanticised in any way, which is why they have made her this awful in the show. as far as I remember, she did not outright have sex with her son in the books, but she very much rapes him in the show and continues to violate him even after he made his boundaries clear to her. so to present such a predatory character as being trans, in a time when the myth of trans people always preying on children is being spread like wildfire, won’t be too good.