In Co-op mode, Islay's REC stat is increased from 5 to 6, due to her base ATK of +1. Islay's passive does not change.
Islay's Hyper, Rival, has a slightly different effect in Co-op. The Hyper can only target enemies and not players, but otherwise functions the same as in Normal mode.
Islay's passive and Hyper are unchanged in Bounty Hunt mode.
Islay's base stats give her 22 starting stars and a markup of +45% at shops.