Data researcher is Doug Mumma doug@mumma.org
Juliana is mentioned in her father's Will (see the notes for Jacob Fry d. 1792) as being deceased, but that she had a living son by the name of John. This means John was born prior to 1792.
http://ftp.rootsweb.com/pub/usgenweb/pa/lancaster/wills/willabstf-g.txt
FRY, JACOB Brecknock Twp.
January 5, 1792 March 31, 1792
Wife: Catharine Fry.
Children: Jacob, Catharine wife of Andrew Zerrerrer, Peter,
Margaret wife of Jacob White, John, Dorothea, Juliana wife of --- Mumma, and Elizabeth.
Grandchildren: John and Juliana Mumma and
Elizabeth and Catharine (children of Elizabeth -- last name not given).
Ex.: Jacob Voneada and Adam Grill.