Thirty million years ago, she was left on the island Santorini, which was Atlantis' building site in a stasis pod whilst the rest of her people left Earth in Atlantis. Thousands of years later, you will find three Trust agents on her Santorini the original site of the City-ship by Atlantis. They used Cassandra Fraiser to open her pod. (SG1: "Transitions")
When she was released from the pod of about ten thousand years after that, she used her amplifier bracelet to create an energy blast that took out the three Tau'ri members of the Trust who had opened her pod. Cassandra Fraiser, whom had been captured by the group, was able to defend himself from the explosion by using her own powers.
Amara would later use her amplifer bracelet to create a wormhole from Stargate Command to Atlantis for her to go to the city to cure the Ancient contagion, running amok. Shortly before her death she gave her bracelet to John Sheppard with the task of submitting it to Cassandra. (SG1: "Transitions")