YOU SAID:
My friend has a rat in her backyard
INTO JAPANESE
私の友人は彼女の裏庭でねずみを飼っています
BACK INTO ENGLISH
My friend has a mouse in her backyard
INTO JAPANESE
私の友人は彼女の裏庭にマウスを持っています
BACK INTO ENGLISH
My friend has a mouse in her backyard
That didn't even make that much sense in English.