I gave Didelphis Alpha a bit of a visual upgrade this time around, moving her teeth back (since possums have those weird big teeth in back) and giving her some long, flowing hair.
As for why a marsupial has mammalian breasts, that's just a visual choice I justify by stating that she's basically Opossum Terminator meets the Androids from Dragonball Z, and her organic body is genetically engineered and includes DNA from powerful female mammalian fighters as well as opossum DNA.