I also think Connie made here decision to leave right after the Tahoe shooting, when you see her clutching her child and glaring at Michael.
I watched GF3 recently. It takes on an almost comical note where Michael's ushering her around Sicily, and the discovery of Tommasino's body puts a damper on the afternoon. She just says, "It never ends...," doesn't leave, doesn't forbid the kids to go near Michael, even sits next to him at the opera.
