1) A Dog's Tale (1963) by Gordon Dorrance, a thrilling tale of Chickie the chihuahua and her adventurous life during World War II. She was with the Joint Chiefs of Staff in Washington D.C., and at Walter Reed Hospital, and was with the K9 Corpse on V-J day. The book was published after the author's death, completed/edited by his widow Emilie Dorrance.
2) How to Raise and Train a Chihuahua (1958) by Estelle Ferguson and Sara M. Barbaresi, distributed through petshops by TFH Publicatioins (TFH stands for Tropical Fish Hobbyist, though they publish even today books on every imaginable pet).
3) Charlie the Chihuahua What's That? A B C (2005) by Mary Swanberg; a chihuahua helps very small children learn to read and to count.
4) The Complete Chihuahua (1947, rev 1950, 1956, and much expanded 1963) by Milo G. Denlinger. This is the 1956 printing.