(written from a Production point of view)
Sienna Spencer (born 1978) worked as additional stand-in for Jessica D. Stone on the Star Trek: Enterprise first season episode "Detained". She was on set on Friday 8 February 2002 on Paramount Stage 9 when Stone's first stand-in, June Jordan, stood-in for Shawna Engert.
Today, Spencer is known as Sienna Spencer-Markles and has been working as chef, food writer, editor, and researcher in the Los Angeles area. She previously attended the California State University in Los Angeles and worked at Disneyland when she was 17. 
Spencer attended the New School of Cooking between 2007 and 2008 and graduated as a certified chef in cooking and related culinary arts. During this time she also worked as journalist for the Edible Los Angales magazine. Spencer worked as segment producer of the radio show "Good Food" at the National Public Radio Station, KCRW, as culinary instructor for Chef's Inc., and as event chef for Goodness Gracious Foods until 2011.
Since 2010, Spencer has been working as public relations manager and media relations specialist for travel, tourism, destinations, events, hospitality, and food for McCue Marketing Communications, LLC in the Los Angeles area.