You didn't give much from that 1900 census in Robertson Co, TX, so I went looking. There's three generations living there, including what appears to be Leah's widowed twin sister Vashti Lance and her boy, Abner too. With that info I went looking.
1880 census Falls Co, TX:
Category: NameRelationship to head of household; Marital Status; Gender; Race; Age; Birthplace; Occ;upation; Father's Birthplace; Mother's Birthplace.
B. W. SHELTONSelfMMaleW48TNFarmerTNTN S. A. SHELTONWifeMFemaleW39LAMidwifeALLA C. W. SHELTONSonSMaleW20TXFarm LaborerTNLA A. S. SHELTONSonSMaleW17TXFarm LaborerTNLA H. M. SHELTONSonSMaleW14TXTNLA G. W. SHELTONSonSMaleW11TXTNLA M. I. SHELTONDauSFemaleW6TXTNLA W. G. SHELTONSonSMaleW4TXTNLA Leah SHELTONDauSFemaleW2TXTNLA Vashti SHELTONDauSFemaleW2TXTNLA
Here's one of their daughters. And that gives you the maiden name of her mother Sarah.
TX Dth Idx thru 1976 --
Name: Mary T. Tirsley Death Date: 21 Feb 1961 Death Place: Waco, Mclennan, Texas Gender: Female Race: w Death Age: 87 years Estimated Birth Date: Birth Date: 09 Nov 1873 Birthplace: Texas Marital Status: Widowed Spouse's Name: Father's Name: William Shelton Father's Birthplace: Mother's Name: Sarah Ann Walker Mother's Birthplace: Occupation: Housewife Place of Residence: Marlin, Falls, Texas Cemetery: Eutray Cemetery Burial Place: Kosse, Texas Burial Date: 23 Feb 1961 Additional Relatives: X Film Number: 2116710 Digital Film Number: 4166565 Image Number: 353 Reference Number: cn 10533 Collection: Texas Deaths, 1890-1976
William and Sarah are on the 1880 and 1870 census in Falls Co, TX and in 1860 in McLennan Co, TX.
If you go to the Rootsweb's WorldConnect site -- http://wc.rootsweb.ancestry.com/cgi-bin/igm.cgihttp://wc.rootsweb.ancestry.com/cgi-bin/igm.cgi -- Type in Shelton, William, died in Texas, spouse Sarah Walker. There are several working on this line. Just be careful some may have just copied from others, warts and all, so I would contact the submitters and see if you can learn about their sources.