I know a guy who has had two knife kills in our recent conflicts, both times when an enemy tried to take/wrestle for his rifle. Rather than fight over the rifle, and with his pistol hand occupied/blocked by the enemy's relative position, he drew knife with weak hand and decisively ended both encounters.
So, yes, this technique can work very well.
But yes, the guy in question is a SOF type, and has had at least some training.
She may already train; if she does not, then she might look for an escrima or arnis class, since they train at fighting with a knife or stick in either hand, or two knives or two sticks.