YOU SAID:
my sister decided to get a cat for christmas
INTO JAPANESE
私の妹はクリスマスに猫を飼うことにしました
BACK INTO ENGLISH
My sister decided to have a cat for Christmas
INTO JAPANESE
私の妹はクリスマスに猫を飼うことにしました
BACK INTO ENGLISH
My sister decided to have a cat for Christmas
That didn't even make that much sense in English.