I think this issue should be legally scrutinised further. JK Rowling's support is helpful, provided she does not back-track through fear from the trans lobby. She could help further by donating towards Maya's crowd-funded legal fees.
From the legal documents submitted by Maya to court it appears her employer objected to Maya using the words "material reality" in relation to male and female as some colleagues objected to and found offensive the idea that there was a material reality for biological sex. The employer seems to be saying that people can identify as whatever sex (as opposed to gender) that they want.
The employer's stance contravenes Section 11 of the Equalities Act 2010, which has sex as a protected characteristic.
Schedule 3 allows services not to include people who have changed their sex per a Gender Recognition Certificate if it can be shown this is proportionate and meets a legitimate end. Schedule 9 of Act similarly allows employers to limit certain roles to those who have a particular sex by birth.
"This paragraph contains an exception to the general prohibition of gender reassignment discrimination in relation to the provision of separate- and single-sex services. Such treatment by a provider has to be objectively justified."
Parliament's Explanatory notes to the legislation state that " A group counselling session is provided for female victims of sexual assault. The organisers do not allow transsexual people to attend as they judge that the clients who attend the group session are unlikely to do so if a male-to-female transsexual person was also there. This would be lawful."
http://www.legislation.gov.uk/ukpga/2010/15/notes/division/3/16/20/7