Annotation: "Carrot-Top" is the more idiomatic English nickname (probably used only for children, by the way). I've never heard "Carrot" used in this way (though I think it's fine to use it in a translation). Note also that you're comparing the top of the person to the body of the carrot, not the top of the carrot, or else the person would have to have green hair!

Another annotation: the term "red hair" is commonly used to refer to people whose hair has any kind of reddish tint.

The nickname also occurs in unhyphenated form "Carrot Top".

Up for discussion: is it "correct" to translate this with the present habitual in English?

For me, прозвали is simple past (i.e., she was given the name), and leaves open the possibility that most people (or maybe all) do not actually call her by it now, even if the possibility is slight.

As such, "whence comes the name" seems appropriate but "so they call her" does not... at least for me. But I would agree that in many contexts one would imply the other, and the translation would be valid then.

I decided to avoid the issue by using "so they gave her the nickname".