Yes, she's certainly cuter than Dagny/Ayn but this is a movie not a documentary. You might convince me if you could cite one or two references that demonstrate that Dagny wasn't cute. Maybe she was. Maybe she wasn't. If we don't know then I pick cute.
Of course if Dagny is really the alter ego of Ayn and we are after strict compliance then it is case closed and you win the argument.
OTOH, I recall that Patricia Neal played opposite Gary Cooper in The Fountainhead. A reasonable person could easily conclude that she was selected by the author because she had a slight resemblance to Ayn Rand but was, of course, quite a bit "cuter". So even the great Ayn Rand fudges in favor of cute. I'm sticking to the cute and talanted even if slightly liberal (I think she is faking it - she's from Kentucky after all) Ashley Judd.