I hated her in season 3, didn't mind her so much in S4, because Edgar Stiles made everyone seem so much less annoying by comparison. Now I love Chloe, I think she's brilliant. I love the scowl, the sarky put downs, the know-it-all-ness and the crush she has on Jack, all so evident to the audience, totally overlooked by the man himself.
I think she's almost as indispensable as Jack at this stage. Even more than with Tony, there'd be an outcry if they killed her off. It's actually hard to think that she wasn't in the first two seasons. Though in some respects, she has taken over the role that Nina had - before we realised she was a villain - that of the techhead who constantly gets Jack out of bother and guides him on his way. But with extra attitude. And a PHD in sarkiness.