Sterling Gates once said on his twitter he better ask Robinson where Supergirl ends up following the cry for justice mini like it had slipped his mind. He's also pretty laid back about these things. Like he's a fan with the best luck and who's in no place to say no to anything.
Robinson said last time that Didio demanded that the superman and batman symbols be represented on the JLA with batwoman and supergirl and its possible he feels more comfortable with mon considering he's writing him in Superman but narratively it may be weird that Supergirl gets switched out so fast or perhaps the league in cry for justice doesn't call itself a league, its just a mish mash of people thrown together during a crisis