Cashell was a member of the the English Channel 2-way relay team called Crosóige Mara, which also included Maeve Ryan, Owen O'Keefe, Eoin O'Riordan, Caitlin Desmond, and Lynne Lynch. They swam under the escort of Michael Oram of the Channel Swimming & Piloting Federation on 13 July 2013. The first leg took the team 10:18:59 exactly, which is just one second faster than team member Owen O'Keefe's solo swim time for the same crossing, and the second leg took 10:10:01 exactly. The total time of 20:29:00 was a new Irish 2-way relay record by over 40 minutes. Through the swim, the team raised €13,250 for the Down Syndrome Ireland charity and advocacy group.