From stopyourekillingme.com:
Delilah Doolittle, a British widow and pet detective, and Watson, her Doberman pinscher, in fictional Surf City (Huntington Beach), California, are featured in:

The Purloined Pooch (1997)
The Motley Mutts (1998)
The Careless Coyote (1998)
The Missing Macaw (2000)
The Canine Chorus (2001)
The Beastly Bloodline (2003)

From FantasticFiction.com:
Sunny Southern California seems an unlikely place for a British widow to call home. But pet detective Delilah Doolittle is probably the least eccentric--if not the most civilized--of Surf City's resident population. With the astute Doberman pinscher Watson sniffing out clues, Delilah follows the trails of missing animals, which often lead to the worst of human nature. The first thrilling pet detective mystery has Delilah Doolittle searching for a champion German shepherd. But when she finds a murdered man instead, it's up to Delilah to collar a killer!