All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
If your wife stepped on the urine while her feet and the floor were dry, then nothing needs to be done. The ritual impurity is not transferred in this case; it is only transferred when there is moisture. If she stepped on the urine with wet feet or the floor was wet, then the ritual impurity is transferred to every place that she is certain that she stepped on with her wet feet afterwards, according to most scholars. In this case, she should purify those spots by pouring water on the spots that she is certain that she stepped on with her wet feet.
However, if there is only suspicion that impurity was transferred to a spot, then it is deemed ritually pure as this is its presumed state (i.e. there is a certain presumption of purity, which is not superseded by suspicion alone).
For more benefit, please refer to Fatwa 85203.
Allaah Knows best.