Exactly. The reason she isn't Spider-Woman any more is because after she outed herself "I preferred Spider-Woman but Spider-Gwen stuck". There's no point in using another codename on Earth-65, because everyone will call her Spider-Gwen anyway. But on 616, her identity would not only be secret, anyone who does find out would be laughed at if they try to tell the press because Gwen Stacy is dead. Not wanting to step on Jessica Drew's toes, she'd need a new name. Taking inspiration from what the Mary Janes said about helping people like a friendly ghost, that'll be why she calls herself Ghost Spider.
All just a theory right now though. I think we'll know for sure what's going on when Spider-Gwen: Ghost Spider #4 is solicited.