Disclaimer - I do not own Buffy the Vampire Slayer, or Stargate: Atlantis
Notes: Fred was never sucked into a portal. She was tapped by the Stargate program and has multiple doctorates.
She'd been there a long time working quietly and efficiently in the background. She was vaunted among the scientists for never having been screamed at by McKay. With her petite form and shy demeanor Fred Burkle was easy to overlook, in fact she likely would have been completely unremarkable if it wasn't for the almost frightening intelligence that could go toe to toe with Rodney when she felt it was needed, and on the rare occasions that she lost her temper, even the tempestuous Dr. McKay backed down. Fred held basically the same place as Zelenka in the scientists hierarchy; she was intelligent, she was skilled, and she had the added bonus of the Ancient Gene. What Fred lacked was self-confidence as a woman. It didn't help that when the military personnel heard talk of the doings of Dr. Fred Burkle most didn't realize that it was the young physicist with the long hair and penchant for Mexican Food.
Still, those that knew Fred well knew that she was the one you wanted by your side in a crisis. Always level headed in an emergency and a crack shot with a gun when she needed to use it, she was a good woman to have at your back. The biggest problem with Fred, was that she had no people skills and tended not to do well with the locals. It was the sole reason she wasn't assigned to a team. So she tried to stay out of the way, often found in her lab surrounded by plexiglas boards hanging in mid air, a dry erase marker in each hand and more tucked in her lab coat pockets. She felt better being able to write it all out by hand, literally surrounding herself with the problems, than by putting her equations into a computer and trying to beat the machine to the answer.
The tiny Texan was a genius. A prodigy of theoretical physics, and downright scary when it came to the actual engineering portion. She could take something apart, put it back together and then duplicate it from scratch. Her ability to turn seemingly common objects into something completely different was what had drawn her to the SGC's notice in the first place. She stood out in the crowd of brains as something special.