Sid was born on Palaven, her family consisting of Vetra, their father and their mother. Their mother left them very early on and lived on Palaven for the rest of her life. Their father was a military man and also left the young turians alone early on after not returning from a mission.
With no parents to speak of, Vetra and Sid survived on the only means they could: smuggling. Vetra, being the elder sister, took the role as head of the family and took care of Sid as best she could. Sid and Vetra were introduced into the Andromeda Initiative when the superintendent, Nakmor Kesh, found their small time smuggling operation and, instead of turning them in, hired them to get her things the Initiative needed to build its projects. After years of running these strange jobs, Vetra asked Kesh what they were for only to be shocked by their contributions to the Initiative. After a referral from Kesh, they used the Initiative to create new lives for themselves.
Damage to Sid's cryo array caused her to be woken early, during the initial disastrous arrival of the Nexus in Andromeda. She witnessed everything that followed: multiple leadership changes and the Nexus Uprising. She was still a minor though, and was still optimistic things will turn out for the better.
Mass Effect: Andromeda
Sidera is a communications monitor on the Nexus, though it soon becomes apparent that is not all she has been up to. She frequently, using her sister's name and contacts, attempts to assist with life in Heleus by aiding others, including several exiles. She has even released cat DNA samples allowing for their production on the Nexus.
Sid later contacts Vetra and Ryder to notify them about settlers being kidnapped. Sid tracked their location to H-047c and wants to help, but Vetra ordered her to remain on the Nexus where she is safe. Nevertheless, Sid followed Ryder and Vetra to an outlaw base where Ryder's squad falls into a trap. To Vetra's confusion, their captor, Meriweather, and her other captives, all claim that Vetra helped the captives escape their outlaw pasts by helping them leave Meriweather's smuggling ring and create new lives for themselves in the Andromeda outposts.
After escaping the prison, Vetra learns that Sid was the outlaws' true benefactor, having used her older sister's name and voice to help Meriweather's indentured servants escape. Sid admits to her role in helping the exiles and also uses her hacking skills to aid Ryder's squad and the kidnapped colonists escape the base. Meriweather found Sid's hidden shuttle however and captured her. When Ryder's squad confronts Meriweather, they find Meriweather holding Sid hostage but they managed to kill her and rescue Sid. Afterwards, Vetra scolds her sister for recklessly putting her life in danger. Frustrated that Vetra doesn't encourage her good deeds, Sid angrily storms off to the Nexus like her sister wanted.
Sometime after Ryder visits Kadara Port, Sid will email Ryder about suspicious findings she's found that implicate some sort of conspiracy against the Nexus. When Ryder goes to speak with her, Sid explains that while monitoring the coms, she noticed that a gang called the Three Sabers has been frequently hitting Nexus outposts and supply vessels with suspicious foreknowledge of Nexus operations. Sid says despite reporting her findings to her superiors, Nexus leadership just mollifies her and doesn't follow through with any investigation. Sid urges Ryder to investigate the Three Sabers and bring the Nexus betrayers to justice.
Should Ryder investigate the Three Sabers, it is revealed that the gang was supplied and hired by Foster Addison to protect Nexus interests but the Outlaws went rogue and started raiding the people they were meant to protect. Ryder and Sid then confront Addison about it and she admits hiring the outlaws was a mistake but urges they keep quiet about it lest it sparks unrest against Nexus leadership or damage relations with the angara. Sid however, believes that the Initiative needs to own up to their mistakes and tell the public. Should Ryder side with Addison, Sid begrudgingly erases the evidence she collected and ceases pursuing the issue out of respect for Ryder. If Ryder sides with Sid, Sid is determined to make sure the truth comes out, resulting in the debacle being broadcasted on the Heleus News Service.