Why is she here? Time is too tight for kissing or gratuitous sex, so there was no need for a love interest. She really does nothing that Matrix couldn't have done himself (I mean, shouldn't he know how to fly a sea plane and puzzle out fueling information? Isn't he one of those guys?), and the rocket launcher rescue could have been cut because, come on, Matrix was too badass to really get arrested anyway. It takes up time that he could have been shooting more of Arius' mercenaries in hilarious and gory ways.
I'd really like to nominate her for worst action sidekick ever, except that I'm sure there's far worse out there. I'm not talking about actual sidekicks, like Chewbacca or Samwise Gamgee, but the untrained citizens who get drawn into perilous situations.
Most of the time, the hapless sidekick is a chick, and usually they just to have her shirt ripped provocatively. But there's quite a few men in the bunch, such as Leo Getz. As of Lethal Weapon 3 and 4, he's absolutely useless, but in Lethal Weapon 2 he was actually worth his space and shrill voice. (No one in the LAPD could figure out they were dealing with South African drug runners until Getz pointed it out. And anyone who says "They live right there!" so that Martin Riggs can later destroy it is OK in my book.)
Even though I defended Willie Scott, she's probably more deserving of the title than Stewardess Cindy. She shrieks and causes no end of problems, but she did save Indy and Short Round from a spiked booby trap. Since Temple of Doom is a prequel, we do owe Willie Scott Raiders and Last Crusade.
But occasionally there's really good sidekicks who pull their weight. Sandra Bullock in Speed should always be held up as the standard. What the hapless sidekicks don't realize is that when a muscled, intelligent guy tells you that some major stuff is going on, and he needs your help, you don't question it. You step up! Bullock does, and so does Samuel L. Jackson in The Long Kiss Goodnight. (I don't think Shane Black ever wasted a sidekick.)
So, let's get down to business in the comments and create a master list of the best and worst of the accidental sidekicks. I know I'm forgetting a few that aided Stallone, Schwarzenegger, Bruce Willis, Chuck Norris, and every other muscled icon out there. But if I remembered them all, there would be no fun left for you.