Canker sores can be triggered by a lot of things, like stress, acidic things, brushing your teeth too vigorously, hormonal changes, allergies. So yes it is possible, but I tend to not believe anything she says.
Canker sores and cold sores are very different. Cold sores are a known virus, and there isn't an exact known reason why cancer sores develop, just known triggers (I work in dentistry.)