"Zij fietst niet."
Translation:She does not bike.
I think it should rather be "she does not cycle". Bike is not really a verb in English.
"bike" isn't really a verb in English it's "cycle".
"Bike" is a sort of colloquialism. The times I have heard it, it has been associated mostly with motorbikes. ("We biked to the next city"= "we went to the next city by motorbike").