Meeting Nina Arianda in person for the first time is very different from meeting her onstage. Instead of the high-pitched "WHA-A-A-A-T?" with which she announces her entrance as Billie Dawn, the classic dumb blonde she plays in the revival of "Born Yesterday" at the Cort Theater, Ms. Arianda offers a low-key, low-throated pleased-to-meet-you. Her honking version of hello — which Charles Isherwood described in The New York Times as a cross between Jean Harlow and Cyndi Lauper — has helped to turn Ms. Arianda, 26, into Broadway's newest darling and won her a Tony nomination for best actress.