Note:  the initial "B" may be hers or her first husband's.

1.  Oklahoma Marriage Records:  Choctaw Nation, Indian Territory.  U.S. Court, Second Judicial Division (online at the McCurtain Genealogical Society web site):

Stroup, B. Mrs. , 44 , Eagle Point , C.N., I.T., to Chastain, John B. , 49 , Eagle Point , 11 Aug 1901

2.  In 1900, there are only two John CHASTAINs in Oklahoma, and neither is obviously our subject.  There numerous STROUPs, but none with given name beginning with "B," male or female.

3.  In 1910, there's a John B. CHASTAIN (age 59) in Chouteau, Mayes Co., OK, but he and his wife (name unreadable) have been married only once, for 36 years.  There's a John B. CHASTAIN (age 62) in Lathamville, Dekalb Co., AL, but his wife is Ruth, and they've both been married only once, for 26 years.  These are the only John B. CHASTAIN's in the entire census within five years of being born in 1852.  Checking all CHAS* in OK born in the 1850s, none is obviously our subject.

4.  There's a John B. CHASTAIN (æ 68) in the 1920 census of Quinton, Pittsburg Co., OK (p. 224A), but he's a widower.