Claim: Kaitlin Olson began her career in an improvisational group.

Kaitlin Willow Olson -LRB- born August 18 , 1975 -RRB- is an American actress and comedian . She began her career in the Groundlings , an improvisational group in Los Angeles , California , and had minor roles in several television series before being cast as Deandra `` Sweet Dee '' Reynolds on the FX black comedy series It 's Always Sunny in Philadelphia in 2005 .   Olson has also appeared in film , with roles in Leap Year -LRB- 2010 -RRB- , The Heat -LRB- 2013 -RRB- , and also provided the voice for Destiny in Finding Dory -LRB- 2016 -RRB- . Beginning in 2017 , she stars as Mickey on the Fox comedy series The Mick .