Is your return flight on the same route? Dublin has what is known as "pre-clearance," which means you clear US customs and immigration in Dublin, rather than the US. However, I've never done it on a connecting flight, nor have I done it with Aer Lingus.

Can someone else chime in here?
* Will she have to collect her bags in Dublin prior to going through pre-clearance?
* I see that Aer Lingus still lands at Terminal 5. If she were on American or United landing at T3 or T1, I know her bags would be checked right through to OKC, but does T5 have an exit that allows passengers to bypass immigration and customs? Will her bags be checked through or will she have to claim and recheck them at ORD?