Trisha Hayes is a student at Albert Einstein High School. She is first introduced in the sixth installment,mentioned as being one of Lana's cronies. In the first book, Mia notices that all of Lana's friends are gorgeous with breasts,meaning that Trisha,too,is just as pretty as Lana.

Known sometimes as "Trish",she taunts Mia in the sixth book,stating that nobody cares if Mia is a princess,because Lana is much more popular than her. She and Lana have a "sisterly love" for each other, but from a comment made by Lana about how "if Trish thinks she's getting Colin Farrell,she's high",Lana believes herself to be more attractive than Trisha.

At Lana's whim,Trisha goes shopping with the former and Mia,and gets a coffee with her. They help Mia to flatter her new breasts in book nine, and Mia realises that Lana and Trisha are actually nice people. Trisha advises Mia to date JP,calling him cute and telling her to simply buy him another cologne,misunderstanding Mia's comment on how JP didn't smell right, as Michael smelled of soap and JP of dry-cleaning fluid. 

On Mia's list of people she loves in the seventh book, Trisha is number 23,000, below a doorman who wouldn't let Mia into the plaza and above Lana Weinberger.