I heard her, but the inconvenience, in my opinion, is marginal, as stated above, given the better routing options.

DCA is not an airport for international travel. You have an airport specifically designed to deliver international travel to the Washington, DC metro area down the street. You should probably consider using it.

Dulles really isn't as bad as people say. I used to transfer through it all the time, and I actually kind of like it. If you absolutely must stay at DCA, then you can take UA out to ORD and go on from there.

If you are only allowed to purchase full Y-fares, I would be more concerned with how many SWUs I was actually getting so I could get out of the Y-cabin, and you may very well end up getting more SWUs with DL than with UA. You get 6 as a UA 1K, then 2 every 50k over 100,000 miles. The difference is that you will always get E+ seating if you are on UA metal, which is 5" more than you'll be getting on any DL flight in economy.