YOU SAID:

My sister sings incessantly

INTO JAPANESE

私の妹は絶え間なく歌います

BACK INTO ENGLISH

My sister sings constantly

INTO JAPANESE

私の姉は絶えず歌います

BACK INTO ENGLISH

My older sister constantly sings

INTO JAPANESE

私の姉は絶えず歌います

BACK INTO ENGLISH

My older sister constantly sings