"She is eating fish."
Translation:Zij eet vis.
If it is "she is eating fish" which is present continous, shouldn't it be translated in the same verbal time? :/
The continuous aspect is not used the same way in Dutch as it is in English. To describe something that is going right now, English always uses the present continuous, but in Dutch one would generally use the present simple.
You can also use the Dutch present continuous here: "Zij is vis aan het eten" is also accepted. But that construction is not taught until later in the tree, and is not necessary to be grammatically correct (unlike in English).