Rosen was born in New York, New York, United States, North America. She grew up in Roosevelt Island, New York City. Her father, a former Creative Director at an advertising agency in Connecticut, has now semi-retired as the operator of a bone fishing lodge in The Bahamas.

Rosen herself has taken up fishing as a hobby; she claims to hold the women's world fishing record for catching a Permit fish.

Rosen shared an apartment for five years with Stella member Michael Showalter.

A regular on the Brooklyn comedy circuit, Ms. Rosen has written and performed two one-woman shows, "Fast and Loose" and "Room for Rent".

Rosen was discovered in December 2000, when Terry's Chocolate named her "America's Whackiest Amateur Comedian".

Rosen co-wrote and performed "It's a Detective Agency and Everyone's English", a play at the NYC Fringe Festival. In late 2007, Rosen revealed that Variety Shac is working on a television pilot for the Adult Swim cable network.

Rosen performs monthly at Upright Citizens Brigade Theater with her group Variety Shac. She has also made the following solo performances:

• "Fast and Loose"
• "Room for Rent"
• "It's a Detective Agency and Everyone's English" (co-writer/producer)
• Invite Them Up (stand-up performer)
• Pie-Hole Comedy Show (regular host, 2000... )