I doubt New 52 Superman is that fast. He is not connected to the speed force and he gets injured by grenades. J'onn is not part of Diana's Justice League and it is implied that he is stronger than all of them put together. The power dynamic is simply not the same in New 52.
And also not being the same Captain Marvel.
Squirrel Girl solo-ing powerful villains is a running gag. It's just a joke. It's not meant to be taken even halfway seriously.
Zeus' lightning is part of Diana's power up, when she removes her bracelets. If anything, it's a disadvantage for her, because it's something Carol can explicitly absorb.