1) Eye to Eye with Dogs: Chihuahus (2004) by Lynn M. Stone. The dog on the cover is named Zora. Introduction to the breed for young readers.
2) Pet Chihuahua (1954) by Tressa E. Thurmer.
3) Yorkshire-Terrier, Silky-Terrier, Chihuahua (1985) by Leni Fiedelmeir, in German, foolishly with terrier instead of chihuahua on cover.
4) This is the Chihuahua by Maxwell Riddle, 1970 reprint, issued in pictorial cloth (1959 first edition had a dustjacket).