Note: This profile is an attempt to reconcile the game Legends with the official cannon. Thus, Alucard is not the father of Trevor Belmont and Dracula had not yet begun his war against humanity at the time of Sonia's battle, and Sonia does not kill Dracula.
For centuries, the Belmont Clan pursued Mathias, though they were unable to find any traces of him. Then in the 1440's, Mathias felt that he had built up enough power to reveal himself to the world and desired to raise a nation in defiance of God. He found the best place for which to resurrect his Castle and killed the ruler of Transylvania, Vlad Tepes, and took his identity. The Belmont clan took notice of this and sent their best men to assault the Castle and defeat the count. They all failed and Dracula launched a strike against the Belmonts and wiped out the remaining women and children and elderly. Only the young child Sonia and her grandfather survived. While she was growing up, her grandfather sensed a great power within her and realized that she may be the one to be able to bring Mathias to justice and stop his ambitions. He made saving her life his top priority and fled with her. The two of them sought refuge in a home of the Totoyan family, who had kept the Vampire Killer whip for three hundred years waiting for the day that Dracula was found. He trained her to use a whip and told her she must only use her powers for good and she frequently sparred with the sons of the Totoyan family.
By her 17th birthday, the Totoyans went on a daring expedition to Dracula's Castle to retrieve the Vampire Killer Whip. Dracula was aware of what they were doing, but was intrigued that a Belmont might still be alive and had his servants follow them home. They mortally wounded the elder Totoyan and killed Sonia's grandfather in front of her. The elder then gave her the whip and announced that he had fulfilled his role and died. With the help of the younger Totoyans, who were wounded badly, Sonia defeated the foes and then set out to face the Count.
On her way to the Count's chambers, she heard a voice that only she, with her special ability to perceive the spiritual beings, could hear. This voice was that of the Poltergeist King, who was known as Rinaldo Gandolfi during his life. He told her in a fatherly tone to find the sacred weapons that were lost in the castle. She was confident in her own power and felt she had no need of the weapons, but the voice explained that even if she defeated Dracula, he would come back some time, and that her descendants would need those weapons. The voice guided her to where they were. She found them and was able to defeat each of the guardian beasts. She was able to convert their souls into magical power and used them against the inhabitants of the Castle.
She then faced the Count. He was surprised by her strength and had to morph into his demon form for the first time in his life. She was able to beat back that form and he reverted to his human-like form. She was about to deliver a killing blow when Lisa burst in the room and begged her to stop and juxtaposed her between the vampire huntress and the vampire. Sonia was taken aback and gave Lisa a long list of crimes that he had been responsible for. Lisa was aghast by the news, which Dracula confirmed, but she offered her own life to spare his. Sonia then sensed that Lisa was with child and told the other two, who had no idea. She said that she would spare Dracula's life if he would swear an oath to God that he would never harm anyone again. Dracula refused to make such an oath, but he would swear by his love for Lisa and for his unborn son. Sonia then forgave him, blessed Lisa's unborn child, and went on her way. The feud between Dracula and the Belmont Clan appeared to be over.
Sonia married one of the Totoyan sons and would give birth to a son. Since he was to inherit the Vampire Killer whip and in order to preserve the Belmont name, her husband insisted that he be known as a Belmont, and was named Trevor Belmont. She would then have another son and named him Christopher Belmont. The new Belmont Clan grew strong, though the people feared their power as they did in the past and they were driven out of their homes.
When Trevor was ten years old, Sonia was whisked away by a mysterious power to Dracula's Castle in the year 1666. It was five years after Desmond Belmont defeated the Order of Shadows and Dracula, and yet the castle stood. The force behind the Castle's power is found to be a powerful countess. She creates a portal that allows Dracula to return to the physical realm without a "proper" resurrection. Desmond, Zoe, and Dolores Belmont rush to the scene to set things right, but are sent through the portal and are trapped in the Netherworld. Without a Belmont on the scene, the forces of light seek out two Belmont's, one from the past, one from the future, to fight against the dual threat of the count and countess. Sonia is able to defeat the countess and Victor defeats the count.