A house book, or Tabien Baan, for a condominium in Thailand is a registration book that lists the legal residents of the property, always blue for a house but some foreigners have yellow ones. But I read The only evidence of ownership for a condo unit is the condo unit title deed
Maybe you need to spend some time on You Tube, to understand the Thai culture and tradition to avoid some big surprises, how you be caring for the family and not one person etc. She maybe very trust worthy and have good education but many don't have either, so please from an expat of many years who spend her time with locals, be on alert, but I wish you well