What is the ruling on a woman's prayer after performing tayammum due to the unavailability of a clean restroom to perform wudu in her workplace?

It is not permissible to perform tayammum due to the uncleanliness of the bathroom, as this is not a valid excuse for tayammum. It is obligatory for you to perform wudu in another place, or for whoever is responsible for cleaning the bathroom to clean it. Otherwise, there is no harm in performing wudu in this unclean bathroom. You must repeat the prayers you performed with tayammum, because they were prayed without a valid ritual purification.