"The girl does a cartwheel."

[crowston]

It seems unfair to ask for a translation of an idiomatic expression without any introduction.

[march]

why in this case 'a' is translated as 'la' and not 'una'? Is that a mistake or not?

[f.formica]

The sentence doesn't mean the girl is building a wheel for a cart, but rather this:

http://cheerleading.about.com/od/gymnasticsandtumbling/l/bl_cartwheel.htm

In English that's called "doing a cartwheel"; in Italian "fare la ruota". Both are entirely idiomatic expressions.

[pont]

It did just accept "fa una ruota" from me, though...

[Teresinha]

Una bella indovinazione! Grazie!