^^according to my friend who's really into the show, the Lori Weston character was producer Peter Lenkov's pet project; it was intended for her to be a "female McGarrett." Consequently, McGarrett's current love interest, Lt. Catherine Rollins, was sent packing. Also sent away for good was Larisa Oleynik, who played Jenna Kaye. It was actually intended for Jenna to permanently join the 5-0 cast, but they killed her off after Weston came on board.
Lori Weston was introduced as a super character, able to do anything that the 5-0 force can do, and this reduced the screen time of the other supporting characters, most notably Chin Ho and Kono, which angered fans of the show, who bombarded Lenkov's Twitter account and CBS with hate mail and petitions were even made online to get rid of Weston. Production insiders also reported that Alex O'Loughlin and actress Lauren German, who played Weston, did not get along, resulting in their lack of chemistry onscreen.
The character's screen time was then significantly reduced, giving her injuries to downplay her abilities and sideline her to 5-0 HQ before booting her off, and Lt. Catherine Rollins was returned to the show. My friend says that German still has one more episode in her contract, so she might return for the finale (probably to be killed off, LOL)