Sarah Jane is the third companion to sneak aboard the TARDIS, the first being Steven,
and the second Zoe. Sarah Jane is an invesigative reporter, and when she and the Doctor
happen to be investigating the same problem in "The Time Warrior" she stows away to
get more info. Yes, the TARDIS can resist an H-bomb attack, but the crew should still
do a little work on remembering to keep the door closed!
Sarah Jane definitely wasn't a screamer. If one of those hideous aliens snuck up behind Sarah and tapped her on the shoulder she'd probably turn around and kick him right in the whatchagahootchies, if he had any whatchagahootchies. So Sarah became more of a partner or at least a sidekick than most of the other companions.
Sarah was a companion for about two years until "The Hand of Fear" in October 1976. After that adventure the Doctor is called back to Gallifrey by the Time Lords and he isn't allowed to bring any non-Time Lords along so he takes Sarah Jane back to Earth.
And...he never came back. Sara menioned in "The Adventures of Sarah Jane" that she waited for him for a while and finally thought he must be dead and gave up. Yeah, these Time Lords are such love 'em and leave 'em types!
Sarah Jane is played by Elizabeth Sladen (born February 1, 1948 in Liverpool). After her Dr Who period, Sarah played in a couple of Dr Who spinoffs, "K9 and Friends" and "The Adventures of Sarah Jane" being two.
Elizabeth died of cancer on April 18, 2011. She was 63.