Salaam respected brother, I know this question has never been asked before but the act ( & due to staunch deen) is still being performed and the obscurity needs to be cleared.
It is not permissible to perform Fardh and Waajib Salaat in the car even though the car is facing Qiblah. (Tahtaawi pg.331; Karachi)
We suggest that if there are no Salaat facilities for women, they should wait for all the men to leave the Musjid and thereafter perform their Salaat
in the Musjid. Alternatively, if the reason is safety, the men should complete their Salaat in the Musjid and thereafter keep an eye to the women while they perform their Salaat outside the car.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai