Letter to Minnie Stilwell from Cora (surname unknown), July 30, 1872

This letter presents another little mystery.  It is from "Cora" (no surname) to "Minnie" (Mary Elva Stilwell).  In it, Cora refers to Minnie as her sister, however, I know of no Stilwell named Cora.  Minnie was 10 years old.

Letter addressed to: Miss Minnie Stilwell, Fond du Lac, Wisconsin 

from Metomen August 2

Metomen  July 30^th 1872

My Dear Sister

I received your kind letter and was glad to hear from you    it found me well yet very lonesome since you went away.  I was glad to hear that you had a good time to the caravan   We went and had a very good time   We had to sit way down on the low seats   Frankie was there   She set on the highest seat   We went all around town   I have not seen her since las Sunday so I couldn’t tell her what you wanted I should   She said when I wrote to tell you to write to her.  Are you going to come home when school commences. 

Mother got home the same night you went away   you can show it to blanche if you want to but don’t unless she ask you to  I cant think of much more today.  Write soon.  From your affectionate sister

                                                                                Cora    

It seems to me that Minnie is once again visiting her sister, Blanche, and her brother-in-law, Frank Munn in Fond du Lac.  Cora is in Metomen, which is Minnie's hometown and where Minnie's parents live.  

Cora mentions a mutual friend, Frankie, who is female.  Update: I discovered from a different letter that Frankie is Francis Cook.  Frankie's mother was Elizabeth Jane Munn, sister to Frank R. Munn.  So Frankie was the niece of Frank and Blanche (Stilwell) Munn.  The Cooks lived near the Stilwells in Metomen per the 1860 federal census.

She mentions Blanche, Minnie's sister.  And she mentions "Mother" but it isn't clear whether she means "my mother" or "our mother."

Cora writes like a young girl, not an adult or a child.  Minnie's youngest sister, Edith May, was only 7 in 1872, so I doubt that she is Cora.  Her next closest sister, Hannah Ruth, was 20 in 1872, so I don't think she is Cora.

I thought perhaps she was a sister-in-law.  The only of Minnie's siblings who were married in 1872 were Blanche to Frank Munn and Annette to Charlie Osborn.  I have not explored Frank or Charlie's families, so perhaps Cora is a sister to one of them.  

Or maybe she is a cousin.  Or simply a friend who was so close to Minnie that they considered themselves sisters.