Yes, Susie Gilbert, which I believe is her real name, and Shawn Ireland, which is not her real name (I believe it's Pam Gilbert), are sisters.
Which begs the question, what did they call Shawn Ireland at work? Did they call her Shawn or did they call her Pam? Calling her by her stage name in real life is kind of weird, but if they call her by her real name, they might screw up on the air.
Incidentally, I've seen signed checks from the actor Eddie Albert signed Eddie Albert, even though his real name was Edward Albert Heimberger. There's a Heimberger Road in Fairfield County and it's named after his dad's side of the family. Even though Eddie Albert wasn't from here, his dad was.