Lynda-with-a-Y Not-Linda-with-an-I-she-got-forcibly-evicted-for-damaging-a-camera was a Potential Companion of the ninth Doctor. In keeping with tradition, she was horribly murdered before her debut story ended.
Lynda-with-a-Y was going about her normal life of watching shitty television when she got transmatted into the Big Brother house by the Game Station. There, she suffered the horrifying and terrible indignity of being a reality show contestant. Eventually, she met the Doctor, which in cases where he goes into the episode with a companion already is legally recognized by the UK as an act of accidental suicide.
Lynda-with-a-Y helped defend the Game Station against the Daleks when they arrived to exterminate everyone (spoilers, btw). Her post was to coordinate defenses with the little screen Adam Mitchell tried to steal information from a hundred years prior. Unfortunately, everybody died as they tend to, and she was exterminated by the Daleks. Unlike Captain Jack Harkness, she was not revived and made immortal by the Bad Wolf at the end, which is weird.
She was pretty comfy and would have made a interesting addition to the current companions. Her being from the future and not modern day would have also triggered Tumblrites to no end. However, her death was kind of needed as yet another gut punch for what was already a pretty grim, dark and nasty finale (at least by nuwho standards).