Alarm went off when my wife started the car. Horn and lights started going on & off. My wife disconnected the fuse to the horn & then the battery was disconnected. That stopped the alarm; we hooked the battery back up & the horn fuse was reinstalled. We tried to start the car, but it only turns over. It won’t run.
Disconnecting the battery on modern vehicles can cause all sorts of problems. One being it may cause the anti-theft system to not allow the engine to start because it believes the vehicle is being stolen. You can read about the problems that can arise here. http://www.aa1car.com/library/battery_disconnect_problems.htm
Tester
She may have been able to stop the alarm by simply pressing the key fob, I’m not sure of that though. I would first try to reprogram the remote to see if that helps solve the issue.
stick the key in the drivers door and turn.