Ok, hmmmm I have stated my theory on Nero on the forum a few times now. But as to who his mom is. I have absouletly no idea. But I do know that it is not Eva. If it was Eva that would make Nero, Dante and Vergil's little brother. And honestly that doesnt fly well with me. And Dante refers to Nero as "kid" so I assume Nero is quite a bit younger than him. I see Dante being around 29 or so in dmc 4. And Nero being around 18 or 19.
And
@ ksubzero and Devil Bane
That girl that you are refering to in code 2 of the manga. I believe to be Alice from code 1. She has the same look. And if I remember correctly, in code 1 Alice chiose to remain in wonderland. She states that she wants to be adult faster. And if I recall correctly I remember the white rabbit (rabi) saying something about that. So the same Alice appears in Code 2. Steals Dante's amulet, and hides. I remember Dante calling her a "Linda Blair wannabe".