Cara Cooper is still relatively new to the Broadway scene (Urban Cowboy, All Shook Up, and now Wedding Singer) and many people toil much longer in ensembles before finally getting cast in lead roles. Look at Michael X. Martin who understudies star-making roles like Don Quixote or Javert and has been doing show for 20 years but still has yet to originate a featured part of his own.
At auditions, Cara (and many others) are up against a lot of pressure to show producers what they can do in a short period of time. She is competing not only against people like her trying to move out the ensemble, but people like Amy Spanger who have already made the transition and possibly even pop/TV/film stars brought in by the producers.
At this point in her career I think she is just glad to be understudying leads and having the chance to go on. Give her more time. I am a fan of hers as well, but getting a role on Broadway is INCREDIBLY hard. This is why 90% of Actor's Equity is unemployed at any given time. This why the cast of shows like Beauty and the Beast and Phantom of the Opera don't change. It's hard work to stay in place let alone move up.
Dean: Can I tell you something?
Lorraine: That depends on what it is.
Dean: I think you're really really pretty.
Lorraine: (after a pause) Ok, you can tell me that.