Did you notice Wm Robinson two pages away from Lee, her husband and daughter on the 1900 census in Archer Co, TX?
The wife might be a second wife, as there are two stepdaughters in the household. This might be your Lucy in 1880.
1880 census Bosque Co, TX:
Category: Name;Relationship to head of household; Marital Status; Gender; Race; Age; Birthplace; Occupation; Father's Birthplace; Mother's Birthplace.
Wm. D. ROBINSONSelfMMaleW31MOFarmerTNTN S. A. ROBINSONWifeMFemaleW30ALKeeping HouseTNTN Robert W. ROBINSONSonSMaleW8TXMOAL Lilly ROBINSONDauSFemaleW6TXMOAL Lucy ROBINSONDauSFemaleW4TXMOAL Lee ROBINSONDauSFemaleW1TXMOAL Elizabeth WARDDauSFemaleW12TN------
Next door, might be a brother to the above Wm:
James ROBINSONSelfMMaleW26MOFarmingTNTN Louisa M. ROBINSONWifeMFemaleW19TXKeeping HouseTNTN Angie M. ROBINSONDauSFemaleW7MTXMOTX Ike GREEROtherSMaleB10TXServant------ Robt. S. PORTEROtherWMaleW60TNMerchantNCVA