I believe my m-in-l mentioned a prominent family named White in the Whitesboro area of Grayson Co, TX. You might want to check the Grayson Co, TX GenWeb site, too. Of course, White is a very common name, too.
Ann's obit said "about" 1890, they probably just rounded it off. Pottawattomie Co, OK was in the IT in 1897, but OK Terr. was formed in 1890 & then it was in OK Terr, until state of OK was formed in 1907.
Did Ann's death certificate give the name of her father? If so, have you checked the 1870 census, when Ann would have been 3 yrs old and in her father's hh? And, did you find Ann & William on the 1900 census, it asks some great questions not on any of the other censuses.