Inside Out (Insiders #1) by Maria V. Snyder

Keep Your Head Down.
Don't Get Noticed.
Or Else.

I'm Trella. I'm a scrub. A nobody. One of thousands who work the lower levels, keeping Inside clean for the Uppers. I've got one friend, do my job and try to avoid the Pop Cops. So what if I occasionally use the pipes to sneak around the Upper levels? The only neck at risk is my own…until I accidentally start a rebellion and become the go-to girl to lead a revolution.