What happened to kate from NCIS and what is her final episode called?

I don't watch NCIS all the time, but i like the show and i was wondering what happened to kate becasue one episode she was there and the next time i saw the show she was replaced by the other girl.


Navy NCIS: Naval Criminal Investigative Service Seasons 1-6 DVD Boxset
CSI Lasvegas Seasons 1-9 DVD Boxset
Supernatural Seasons 1-4 DVD Boxset
Scrubs Season 1-8 DVD Boxset
Battlestar Galactica Seasons 1-4 DVD Boxset
smallville season 1-8 dvd
doctor who seasons 1-4 dvd
one tree hill seasons 1-6 dvd
star trek enterprise seasons 1-4
The sopranos seasons 1-6 dvd
boxset4less

family guy seasons dvd box set
the simpsons seasons dvd box set
how I met your mother seasons dvd box set
friends seasons dvd box set
desperate housewives seasons dvd box set
Rurouni Kenshin seasons dvd box set
The X Files seasons dvd box set
Ally McBeal seasons dvd box set
Babylon 5 seasons dvd box set
Firefly seasons dvd box set
Lost seasons dvd box set
Grey's Anatomy seasons dvd box set