Surname "Bais" in Zacatecas

My great grandmother was Loreto Bais. Born in Mexico somewhere around 1868, she eventually settled down with a Tereso Sifuentes (born around 1865) somewhere in Zacatecas. It is said that they were both married with children, before somehow becoming single and finding each other. I don't know when they got together. I do know that they had several children, at least 6. I can only find some of their children's baptism certicates, showing births in northern Mexico, mostly in Monterrey, Nuevo Leon between 1899 and 1915.

I've seen a photo of Loreto Bais, she was obviously an indigenous woman. Oral history says she was Yaqui, but those who say so really don't know for sure. I did find out through a border crossing record that she was born in a town named Agostadero. The death certificate says she was born in 1868 to Andres Bais and Antonia de Lira. I'm unsure of the exact spelling of the name Bais.

Does anyone have any kind of information that could help me find where Loreto is from, or anything about her lineage? Or anything related to indigenous peoples with the last name Bais?

Thank you,
Roberto