
She was not the first woman
Mitochondrial Eve sounds like the first mother of humanity. She was not the first woman and not the only woman alive in her time.Mitochondrial Eve: What She Really Means

So who was she?
She was the most recent woman from whom all living humans descend in an unbroken line through mothers only. Follow mother to mother to mother, and all those lines eventually meet at one woman.Mitochondrial Eve: What She Really Means