Anna was a Goa'uld/Human Hybrid, created by Dr. Keffler, out of the DNA from the Goa'uld Sekhmet as a science experiment to unlock Goa'uld secrets that could potentially save Earth from a Goa'uld attack.
She was held by Keffler in a clear glass box and was never allowed outside of the secret Rogue NID facility in Los Angeles where she was created.
Her attempt to find the deactivation code for an Ark bomb caused Sekhemet to regain control one last time, allowing her to escape the cell.
Eventually Dr. Daniel Jackson discovered the code among Anna's charcoal drawings. At some point Anna regained control over her body, hunted down Keffler and, recognizing how evil he was, killed him.
Afterwards Anna activated a failsafe device inside her own brain, killing herself as well as the Sekhmet personality that was inside her. (SG1: "Resurrection")