ALTERNATE VERSIONS
Only a small number of alternate reality versions of Sersi exist due to so many being murdered by Proctor. Of the handful of alternate versions that have been seen, they are almost exclusively similar to Sersi, as she appeared in her early days with the Eternals.
Proctor's Reality
Sersi was an Eternal who had heard of Proctor's band of heroes known as the Avengers. Unusually for an Eternal of Olympia, Sersi ventured to New Amsterdam and requested to join the team, and 
immediately chose Proctor as her Gann Josin. She fought alongside the Avengers for some years, with Proctor at her side... until she grew bored. She left, seeking new adventure, and broke the Gann Josin, leaving Proctor alone with his thoughts. She was later found by Proctor, who grew mad after embracing his Ebony Blade's curse, and was murdered by the man who loved her. [Avengers (1st series) #374]