The Irex is (according to JW) bigger and smarter then the Trex, it also has camouflage so Pacifica would struggle to find it. The camouflage would work until Pacifica lands a strike on the Irex
Yeah, The Irex would be able to get a few attacks on Pacifica, soon it would go for a bite and Pacifica would throw a splat bomb into the Irex's mouth. The explosion wouldn't kill the Irex but the ink going into the Irex's digestive system would harm it