That would imply that IAD has a train to match the Narita Express. Not so. [sigh]

To return to the original discussion, IAD would be a little less of a nuisance if the OP's friend were to fly B6 or VX than UA, owing to the crumminess of UA's C/D terminal. But overall, if she's willing to trade layover time for commute-from-IAD time, she will probably find DCA much more to her liking. Especially if she takes BART--Metro fares and tickets work almost the same.

Just don't have her book an itinerary that requires making the last flight to DCA from ORD.