The Protea Specter is a boss encountered at the end of "The Deadlock Protocol" quest; she is a mechanically difficult boss that has 4 health-gates and uses the Velox & Gunsen. The steps listed below will teach you how to defeat her:
1.) Build a full Charge with the Xoris by killing 3 specters with the Xoris.
2.) Deplete Protea's shield & health-gate fully by damaging her. (If you find yourself in close combat, you can perform a slam attack while mid-air by looking down at the ground and pressing the melee key/button; this will stun her for a brief moment).
3.) After you damage her, she will use her Temporal Anchor ability to regenerate her health; you must disrupt this regeneration by using your fully charged Xoris by throwing it at her (press and hold melee) and detonating it mid-air by pressing alt fire so the blast will hit her.
4.) Repeat until the Protea Specter is dead.