"They are reading the book for the girl's sake."
Translation:De leser boken for jentas skyld.
A small newspaper database search can show you the frequency relationship between "jente" and "pike".
"jente"(and all forms, both m and f) are 48,5 times more frequent than "pike" (all forms).
And even though "pike" have legal feminine forms, it is (at least in the East) associated with riksmål, and the newspaper database showed 0 instances of "pika" (and that's with 15908 instances of "jente"(all forms), and 3768 instances of "jenta"!).
http://avis.uib.no/avis (simple version)