I was surprised by that Guardian article as well. It did sound like they were trying to be neutral. Even calling someone a 'gender critical feminist' rather than a 't*rf' is a promising step.
Gender-critical feminists disagree with the view of some LGBT activists that gender identity should be prioritised over biological sex in terms of law-making and policy. They fear sex is being argued into non-existence and that this will erode rights hard-won by women in the face of historical biological discrimination.
Regarding why Marion Millar is being prosecuted:
Her Twitter account, which she said she locked on Thursday because of abuse, includes robust defences of gender-critical positions and calling for certain LGBTI activists to be kept away from schools and children.
But Glinner has been 'reliably informed' that she's being charged over a picture of a ribbon.