September 1st draconequus is Princess Eris, she's a canon character in the comics and is the mirror verses lord of chaos. In my AU she is a benevolent character that is referred to as Discords "cousin", although there's no real familial ties. She is a close family friend of the Dozycord family and is usually referred to as Auntie Eris by Discord and Dozys kids or just Eris in lieu of Princess Eris. She does come from a different universe and visits occasionally. Her canon design is different and this is my personal design of her.
In her universe she might have grown up with or known her universes version of Discord when they were young, but something happened to that Discord so she took the role of Lord of Chaos in that universe. Through magical exploration she finds the dozyverse Discord when he needs a friend the most after the draconequus are destroyed (another part of my AU I'll explain later in a comic) and she comforts him and he comforts her in his own way too. They're basically just able to lean on each other when they feel alone. But they can never stay in each others universes for long.