Now that I think about it, Ivy ending up in that sewer felt really contrived. Up until now, Ivy has mostly kept to herself unless the plot called for her to interact with Selina or someone else. As far as I can tell, she never expressed interest in getting involved with Selina's criminal activities, so her pleading to join in and subsequent capture just felt like a way to end up in that predicament.
That way, when Ivy emerges as Maggie Geha, it should be some big surprise or revelation, but it isn't. That's my thought, anyway. If Ivy had been asking to join in Selina's adventures in the last two seasons, I could see her snooping on Fish, but from what I remember, the girl has just done her own thing.