She is Sonya's mother, and is mentioned a few times by Lazarus. She made no physical appearance, since she supposedly died in an accident, although a villager in the Ilias Cont. East Tartarus did mention she was "dressed like a slut".
In the original timeline, she and Merlin were killed by Alice.
In the upcoming event teaser, Nero hypothesize that Sonya was transformed as an apoptosis as early as her presence in Karen's womb.