Cassandra is an alien child from P8X-987, the world known as Hanka. Her people were wiped out by Nirrti. Dr. Janet Fraiser adopted her.
Cassandra was rescued from Hanka by Capt. Samantha Carter, forming a deep emotional bond with her. Carter chose to stay with Cassandra rather than leave her to die alone when it became clear Nirrti had used her as a Trojan horse to carry into the SGC a weapon of mass destruction. Fortunately, they were able to save Cassandra. Dr. Janet Fraiser adopted her and Jack O'Neill got her a dog. (1.15 "Singularity")
When Carter was invaded by the Tok'ra Jolinar, Cassandra was able to sense the presence of the symbiote because of the naquadah in her bloodstream left over from the bomb Nirrti had implanted within her when they found her on Hanka. After Jolinar sacrificed her life to save Carter's and Carter became extremely depressed from the loss, Cassandra played a key role in her recovery. (2.02 "In the Line of Duty")
About a year after saving Cassandra, Daniel Jackson was transferred into the alien Ma'chello's body. He insisted that SG-1 ask him questions that only Daniel would know to prove that he was in the old man's body. Carter asked him who Cassandra was, and he answered, "She's a twelve-year-old girl we found abandoned on P8X-987." (2.18 "Holiday")
Cassandra later became a victim of Nirrti's genetic experiments to engineer a superhuman host, developing telekinetic powers at her 16th birthday. She was receiving a kiss from her boyfriend Dominic when the powers were first manifested. The powers continued to increase and they almost killed her. SG-1 was able to capture Nirrti and get her to cure Cassandra, but the cost of this cure was allowing Nirrti to leave to eventually perform her experiments on others. (5.06 "Rite of Passage")
When SG-1 was accidently thrown far into the future in their attempt to get back to their present time after being thrown back to 1969, Cassandra met them in the abandoned stargate room and sent them back. She said that she wasn't able to tell them everything about the future, but assured them that their journey was just beginning. She was able to activate the stargate with a small device she wore on the back of her hand. (2.21 "1969")
When Dr. Fraiser was killed in the line of duty on P3X-666, Cassandra had most probably finished high school or had begun college. Carter stayed with Cassandra immediately following her mother's death, but Cassandra most likely is on her own now that she is over 18 years old. (7.18 "Heroes Part 2")
Cassandra was going through an unspecified "hard time" approximately two years later (9.07 “Ex Deus Machina”). Samantha Carter took a job with more flexible hours as head of Research and Development at Area 51 in Nevada to be with Cassie. Therefore, it appears that Cassandra lived or went to school somewhere near Area 51 during this period. Presumably these issues are now resolved, since Col. Carter returned to the SGC in Colorado.
- 1.15 "Singularity"
- 2.02 "In The Line Of Duty"
- 2.18 "Holiday"
- 2.21 "1969"
- 5.06 "Rite Of Passage"
- 7.18 "Heroes Part 2"
- 9.07 "Ex Deus Machina"
- Cassandra at age 12: Katie Stuart
- Cassandra at age 16: Colleen Rennison
- Cassandra of the future: Pamela Perry