Is it permissible for a woman to perform tayammum if she is unable to perform wudu' due to the difficulty of using workplace restrooms and the presence of vaginal discharge, which delays her prayer until she returns home before the 'Asr athan?

These secretions nullify ablution (Wudu'). It is not permissible for you to perform Tayammum (definition) (dry ablution) as there is no loss of water or inability to use it. Rather, you must perform Wudu'. It is permissible to delay the prayer until your return, provided that you are able to perform it before its time expires.