The thing is, Abby's previous mental condition was being treated with Medication that was not the right one. That is why she went with her grandmother, who got her the right kind of med, which helped get her back to more or less "normal". The recent stay with gramma did seem a bit ridiculous, as Abby was suffering a different sort of mental breakdown. However, at least Laura was very familiar with what Abby had been through, and Abby trusted her.
With Chad now, this is a different story entirely. O.K. he did not catch on first time on the DID, but he was around when she exhibited the behaviors, hairstyle changes, etc. But currently, he has seen absolutely NOTHING of any of it, only has Gabi's stories, comments, etc. And the one, and only one, that Kate came up with, but no one saw. Not a single other person saw it, including Stefan, not Jen, JJ, Julie, Doug, Stefan, the servants, Chad, Eric, Maggie, NO ONE! Just the tales from Gabi. When Abby protested, talked of being drugged, etc. no one thought for ...wait a second now. And thus Abby played right into Gabi's hands, divorcing Chad, marrying Stefan. Foolish, for sure.
But she was desperate to stay out of Bayview. Her only hope was Marlena, who was recovering and unable to see her. And then Chad further betrayed her, swapping the baby Stefan thinks is his for Stefan's promise to commit Abby. Horrible story, horrible sequence of events, what surprises me is there ARE docs at Bayview. So how come they could not verify she was fine?