Is it permissible to pray sitting in a car when it is impossible to find a women's prayer area?

Your action is incorrect because standing is one of the pillars of prayer.

Praying obligatory prayers in vehicles is not permissible except under two conditions: fear of the obligatory prayer's time expiring before reaching the destination, and inability to dismount and pray on the ground. If these two conditions are met, then praying is permissible, based on the verses: "Allah does not charge a soul except [with that within] its capacity" (Quran 2:286), "So fear Allah as much as you are able" (Quran 64:16), and "He has not placed upon you in religion any difficulty" (Quran 22:78).

One must face the Qiblah throughout the entire prayer if possible; otherwise, one should fear Allah as much as one is able.

As for supererogatory prayers, it is permissible for a Muslim to pray them in vehicles, no matter which direction the vehicle is facing, even if one is able to dismount, due to the hadith of Jabir that the Prophet (peace be upon him) "used to pray voluntary prayers while riding, not facing the Qiblah." However, it is preferable to face the Qiblah when beginning the prayer (during the takbirat al-ihram).

Praying an obligatory prayer while sitting, despite being able to stand, is not permissible due to the general meaning of Allah's saying: "And stand before Allah with devotion" (Quran 2:238), and the hadith of Imran bin Husain: "Pray standing; if you are unable, then sitting; if you are unable, then on your side."