Even though I fly UA a ton, I don't transit Houston often at all (2 or 3 times I can recall). I have a friend who is looking to fly from IAD to IAH to pick up the morning NRT flight. She'd have a 40-minute connection and two teenage kids in tow. Looking at maps of IAH, I assume she's likely to arrive into C or D and go out of D or E. I can't recall if all of those are easily connected and the maps online I found don't immediately show whether there's a walkway between D and E that's airside. I'm 99% sure she's fine but since I'm not familiar with the airport I figured I would ask those UA folks who have more IAH experience.