2004 Pontiac Grand Am security system

My daughter just drove 2 1/2 hours from home to attend a wedding and while she was driving the security light came on. She lost her remote a few years ago but has never had a problem starting the car. They got to the hotel and when they came out the car wouldn't start. The battery is fine but obviously the ignition security system has set and is apparently keeping her from being able to start the car. I've been in the car business for twenty years and remember something about disconnecting the positive terminal of the battery and reconnecting it will reset the system. Please help.