She can file AR-11 any time online in 5 minutes and get instant confirmation. Technically she can do it before or after N-400, it doesn't matter. But I'd do before.
Also, if she already lives in the state for over 3 months, she doesn't need to wait for 3 months after filing AR-11. Residency is not proved by filing AR-11. It's proved by having utility bills, driver's license with correct address, taxes filed in the state. Does she have all that?