YOU SAID:
Bella has to do her work by herself
INTO JAPANESE
ベラは自分で仕事をしなければならない
BACK INTO ENGLISH
Bella has to work herself
INTO JAPANESE
ベラは自分自身を働かなければならない
BACK INTO ENGLISH
Bella must work herself
INTO JAPANESE
ベラは自分自身を働かなければならない
BACK INTO ENGLISH
Bella must work herself
That didn't even make that much sense in English.