My first thought is that something happened to Elisa Agens' parents that
brought her to live with the Bowers. Maybe she is a niece, or even a young
sister to Susan.
If there is a Soundex to the 1850 Iowa census, you could check that for the
Agens name; depending on the month of her birth, Elisa could be on that
census with her parents. Just a thought. Good luck in your quest.
Pat (in MN)