Trisha Delaney was the sister of Rob Delaney.
Rose Tyler knew her as "Trisha from the shop". Mickey Smith claimed to have started going out with her when Rose was gone for long periods of time with the Ninth Doctor. Rose, however, knowing the two of them and thinking "that's never gonna happen", thought Mickey was using Trisha to get back at her, and that "It's got nothing to do with Trisha." Nonetheless, when Rose returned to 21st century Earth in the TARDIS and "pick[...] up the phone", Mickey said he came running for Rose and would "sit here for the rest of [his] life waiting" for her. (TV: Boom Town)
One Wednesday, Jackie found that Trisha along with the rest of her neighbours had gone missing. In reality, she was being isolated from N-Space by the Harvesters in their plot to lure the Doctor and Rose. (AUDIO: Wednesdays For Beginners)