L.H.
Fever blister is called herpes type 2. It is a kind of virus living in human's body and when you've weal immune system or lack of sleep you're tend to get it. Fever blister is aero-forbic. Try to make her rinse with a little bit of salty water off and on, especially after eating. Keep it clean and dry. Discard the toothbrush immediately and replace a new one. Yogurt seems to help and keep away from nuts, chocolate, peas, or spicy food. If I had blister, I normally take Lysine (amino acid) and it really help. And good luck!