Not much is known about the Duchness of Solenna. At some point, she married the Duke of Soleanna and had a daughter with him whom they named Elise the Third. At least ten years prior to present day however, she died under unspecified circumstances.
The Duchess of Soleanna's death was a tragic event for her family. For Elise, the loss of her mother left the young princess with much grief which would weight heavily on her heart for over a decade. The duke himself, while not showing it, was also deeply affected by the duchess' passing. Supposedly, in an attempt for him and Elise to be reunited with her, the duke launched the Solaris Project, an experiment that would allow them to control time with the kingdom's patron Solaris so they could alter history and prevent her death. However, the experiment failed with catastrophic results which split Solaris into Iblis and Mephiles the Dark.
According to Elise, the Duchess of Soleanna was a compassionate and kind ruler, holding a great deal of love for her country and its people. She was also apparently a beloved mother and wife as both Elise and the duke were deeply saddened by her death and wanted to be with her again.
↑ 1.01.1Black, Fletcher (14 November 2006). "Born of Fire". Sonic the Hedgehog: Official Game Guide. Prima Games. p. 4. ISBN 978-0761555100.
↑Sonic Team, Blindlight (24 November 2006). Sonic the Hedgehog. Xbox 360. Sega. Area/Level: End of the World. "Duke of Soleanna: Look, Elise. This is Solaris, the flame of hope. / Princess Elise the Third: It's so beautiful... / Duke of Soleanna: When the flame has grown large enough, our world will change. Solaris will allow us to control time and move through history. People will be able to rectify past mistake and avoid bitter fate. / Princess Elise the Third: Will we be able to see momma? / Duke of Soleanna: Yes, Elise. We'll both be able to see your mother once again."
↑Sonic Team, Blindlight (24 November 2006). Sonic the Hedgehog. Xbox 360. Sega. Area/Level: Tropical Jungle. "Princess Elise the Third: It isn't sometimes, but I love this country. Everyone in the castle, the children, all my citizens really... The same love my late father and mother had..."