Games : Who is angels mother? (Borderlands)

I played the 'snap' out of the borderlands series and really know much about the games. But after the pre-sequel I still have one big question: Who is angels mother? Since we only know about one girlfriend Handsome Jack (who is angels father) had, Mad Moxxi I'd say that she is angels mother but that would not make much sense to me. Does anyone know more about this question or has anyone encountered some echo devices, that could enlight me?

Thanks in advance.