There are no customs/immigration issues..she can go right to her connecting flight. However it's quite probable she'll be arriving in the United Express A terminal and will need to take a train or mobile lounge to the C or D gates. And cutting an already short connection even further is risky. Yes the trip is long, but due to the schedule change UA would likely allow her to change to the next earlier RDU-IAD fllight for free. If it were me, I'd switch even if it makes the journey a bit longer.

Edited: Looking at the RDU-IAD flights for today.. it appears none of them arrive at the A gates. They are all in either C or D (even the Express flights). This definitely helps, but I still would make the change to the earlier flight that arrives at 3:23pm (that's the time for today at least).