Details about her early life are unknown aside from being born a stray. However, it is known that she eventually joined up with Riley and his gang of stray dogs. She apparently has a rivalry with Ashcan and Pete, two vicious junkyard dogs, given her comments to them.
She meets Chance (who turned tail and fled earlier, due to mistaking Riley's Gang as reinforcements for Ashcan and Pete by Sassy) when she tried to bring him back to Shadow and Sassy. After tackling Chance in an alley, Delilah explains why she was chasing him. The two dogs later spark a romance together, though Riley soon finds out, much to his displeasure. Delilah refuses to listen to Riley when he tells her that she shouldn't be with Chance because he is a housepet. Delilah also refuses to listen to Shadow when he tells her how Chance behaves at home. However, due to Chance's unruly antics, he is soon captured by Jack and Ralph, two dogcatchers who drove a blood-red van. Although Delilah and Riley's Gang save Chance from the blood-red van and its drivers, she is forced to turn down Chance on account of what Riley and Shadow had said.
She eventually decides to quit Riley's Gang (which Riley presumably allowed her to do) and travels over to the Seavers' house, using her smell and her heart. Chance is overjoyed to see Delilah again, and the two dogs greet each other affectionately. Jamie then befriends Delilah and asks his mother and father if she can stay, as do Hope and Peter. Their parents ultimately agree, and she is adopted as a member of the Seaver family, much to Chance's delight.