I did a bit of census research and it looks like Martha always reported she was born in Iowa. Here's what I found--hope this gives you some clues to work with:

1900 Payne County, Oklahoma, Stillwater City, ED 190, 8-9 June 1900, pg. 190A/5A?
80/88 McAlister, John R., head, w, m, April 1837, 63, m/25, IN,KY,NC, Farmer
Martha E., wife, w, f, Sept 1855, 44, m/25, 4 children/4 living, IA,NY,England
James, son, w, m, July 1882, 17, single, MO,IN,IA, Farmer
Bennie, son, w, m, Nov 1891, 8, single, MO,IN,IA
Bertie, son, w, m, Feb 1877, 23, single, IA,IN,IA, Farmer
Eddie, son, w, m, May 1879, 21, single, MO,IN,IA, Farmer

1910 Pottawatomie County, Oklahoma, Shawnee City, Ward 5, ED 226, 25 April 1910, pg. 154B/14B:
1122 Whittaker Street
316/327 McAlister, Martha E., head, f, w, 53, wd, 4 children/4 living, IA,IA,England, Own income
Ben H., son, m, w, 19, single, KS,IN,IA, Track walker/Railroad

Also listed on the same page is a James Whitaker that appears to be the oldest son from the 1900 record:
1111 Whittaker Street, 315/326 McAlister, James, R, head, m, w, 27, m1/5, MO,IN,IA,Contractor, wife Julie B, 22, KS & Lorena, dau, 3, OK

1920 Pottawatomie County, Oklahoma, Shawnee City, ED 234, 27 Jan 1920, pg. 158B/14B:
257/282 McAlister, Ben, head, m, w, 28, married, OK,US,IA, Laborer/section(?)
May, wife, f, w, 24, married, OK,PA,NE
Note: Cannot locate Martha E. in 1920

1930 Pottawatomie County, Oklahoma, Shawnee City, Ward 4, ED 47, April 5, 1930, pg. 164B/2B:
309(?) East Main Street
33/44 McAlister, Ben F.(?), head, rents/$35, m, w, 39, m@20, OK,IN,IA, Proprietor/Dry Goods store
May, wife, f, w, 34, m@21, OK,KS,KS
Doris, dau, f, w, 6, single, OK,OK,OK
Mattie, mother, f, w, 73, m@20, IA,NW,England

The next time I go to the Shawnee Public Library I will see if I can locate an obit for Martha if you do not have one.