Costello was the first woman (solo racer) in the history of the Isle of Man motorcycle races to stand on the podium when she took third place in the Ultra Lightweight category of the 2005 Manx Grand Prix.

In 2004 at the Isle of Man TT races Costello achieved a Guinness World Record by becoming the fastest woman to lap the Snaefell mountain course at an average speed of 114.73 mph.

[4] For 2023, Costello was expected to race in the Sidecar TT under Faye Ho's banner, but was sidelined with injury after a practice accident riding a Supertwin solo machine.

Initially it was her race press releases that were published in the local newspapers but her ability on the racetrack led to an invitation to join Motorcycle News and Performance Bikes on road tests.

In 2012 Costello also worked as an occasional guest instructor for The Bike Experience, a charity organisation dedicated to helping motorcycle riders who have suffered spinal damage to ride again.