I lived at St Joe's from 1949, not quite 4 yrs old, until 1959.
You're correct about the Diocese of Superior being a possible source of records. However, I think getting any info from them would be difficult.
I had a similar situation where 3 sisters and 2 brothers were also in the orphanage (technically.. it was called a "Childrens Home") and another sister was put in a foster home. Until I was about 10 years old, I had no idea that I had another sister. The nuns who ran the place did their best to deny us any knowledge of her.
I believe the building was torn down 2 or three years ago.