It is presumed these three names represent the same person, Agnes R. Allyn, b. MA, abt. 1850, seen living on the 1880 Census [Ed 306, P 323, Line 11]
with her family at 134 Chestnut St. She was the daughter of Rebecca B. (Parks) Allyn (who also contributed to the book) and Anderson Allyn, b. abt. 1820.
In addition there is a recipe attributed to Mrs. Agnes Allyn, Molasses Drop Cakes that may be a typesetting error of using "Mrs." instead of "Miss" — No other Agnes Allyn was found in the 1880 or a later Census that would be an appropriate fit. Any corrections are welcome.