From these records it looks like she had 2 sisters. It also looks like her father Levi died the year she was born, so it's unlikely that if he married Persis Hamilton in 1804, there were more children - unless her mother remarried?
Persis Adams Bemis Find A Grave Memorial# 105466812
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=105466812
Birth: 1808 Death: 1874 Beloit, Rock County, Wisconsin
Wife of Foster Bemis Find A Grave Memorial# 105466457
http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=105466457
Birth: Jan. 18, 1808 Spencer, Worcester, Massachusetts,
Death: Dec. 6, 1881 Beloit, Rock County, Wisconsin
SOURCE: United States Census, 1850," database with images, FamilySearch (https://familysearch.org/ark:/61903/1:1:MD9H-XQ1), Persis A Bemis in household of Foster Bemis, Spencer, Worcester, Massachusetts, United States; citing family 171, NARA microfilm publication M432 (Washington, D.C.: National Archives and Records Administration, n.d.).
Foster Bemis M 42 Massachusetts
Persis A Bemis F 41 Vermont
Lucy A Bemis F 19 Massachusetts
Persis J Bemis F 15 Massachusetts
Alvan Bemis M 12 Massachusetts
Lorinda F Bemis F 10 Massachusetts
Charles F Bemis M 7 Massachusetts
Brookfield Births
ADAMS, Persis Nichols, d. Levi and Persis, Sept. 8, 1808. In Richford [VT. ?] [dup.]
ADAMS, Lourinda, d. Levi and Persis, May 22, 1806.
ADAMS, Mary, d. Levi and Persis, Sept. 5, 1804.
Brookfield Marriages
ADAMS, Persis and Foster Bemis of Spencer, Feb. 4, 1830.
ADAMS, Levi and Persis Hamilton, int. ––– ––, 1804.
Brookfield Deaths
ADAMS, Levi, s. Amos and Ruth, July 5, 1807, a. 24 y. 10 d.
ADAMS, Levi, h. Persis, July 5, 1808. (Perhaps same as next above.)
SOURCE: Vital Records of Brookfield Massachusetts to the Year 1850, F. P. Rice Publ., Worcester, MA, 1909
