AoS13

This is in relation to the novel so the details might change since there are a number of differences but………………

Her name is Harari Aakman, Celphis' biological mother, she appears in chapter 69 of the novel.

She left everything behind and ran away, finding Celphi repulsive

And worst of all, it was Celphi who let her into the manor. When Pereshati realizes that she's Celphis’ mother and that he's the one who let her in, she immediately goes to see him.

Meanwhile, Harari tells Terdeo (who asks if she's thought about Celphi being there) that she doesn't love Celphi, that she'll never love him and that if she'd taken him with her, she'd have killed him.
She will also say that Terdeo and the whole family are not victims of the curse but murderers, that they love to kill and deserve to die.

She's come to the duchy to see Pereshati because she can't just sit by and watch another victim like her happen because of Terdeo.
She wants to convince Pereshati to leave, but Pereshati will put her in her place. Pereshati will tell her that she's trying to fulfill her selfish interests by pretending to save her, to use her to fulfill her need to attack the family.

And Pereshati finally tells her that she won't abandon her son as she has done.