She joined the women's 'auxiliary'. [=a group of women who do work for a church, hospital, etc.]
a sailboat with an 'auxiliary' engine
an 'auxiliary' police force
(..) Drop us down underneath them, Sulu. - Sir, there's another Federation ship. - Destroy it too. Fire torpedoes. Captain, they're locking torpedoes. Divert auxiliary power from port nossel to forward shields. - Sulu, status report. - Shields at %. Their weapons are powerful, sir. (..)2009 Star Trek