Sandra Martin was an unseen villainess mentioned in "He Said She Said", episode 1.16 of Sue Thomas: F.B.Eye (airdate April 27, 2003). She was a drug addict and the frequent client (and presumed lover) of corrupt DEA agent Pete Hadley.
The episode had Sue Thomas being falsely blamed for a botched drug bust Pete was helming that resulted in an agent being killed, with Pete falsely claiming Sue had failed to communicate to him that the agent was in danger. Sue's FBI team began working to prove her innocence, uncovering in the process Hadley's status as a corrupt agent who stole drugs from busts he was involved in to sell on the streets.
Sandra was discovered as a possible lead and the agents began working to locate her, with Jack Hudson and Bobby Manning coming into contact with two of her friends, Missy and bartender Sammy. Later on, though, the two learned from Sue that Sandra had been found dead, with the agents confronting Missy with the information.
Cornered, Missy fearfully revealed that she knew Pete had killed Sandra, revealing that Sandra was Hadley's customer and girlfriend and that Sammy worked for Hadley as a mole. Missy also revealed Sandra as an accomplice in Hadley's drug selling operation, as he often had her do deliveries for him, with Sandra even beginning to work with Antwan Drummond (a dealer Hadley worked with). While Hadley's motivation for killing Sandra was never revealed, it can assumed he did so to keep his criminal activities hidden.