HSV-1 is the virus that causes cold sores or oral herpes. You can get the sores on the mouth, interior of the mouth, but can also show up on the side of the face or in the nose. It is very common for young children to get exposed to this virus. Once you have it, you have it for life. There is no cure. More people have this virus than don't. If you have ever had a cold sore, then you have it. Some people get one cold sore and never see symptoms of the virus again. Others get frequent break outs. The virus lives in the nerves and sometimes it just reactivates. The outbreak usually lasts 7-10 days.
The virus is very contagious. If your daughter or someone else touches the sore and then touches another mucus membrane it can spread to that area. These are the moist areas of the body such as the nose, eyes, mouth, and vagina. Be very careful to have her wash her hands if she touches her mouth or if others do. She could even get these sores in her private areas if she were to touch her mouth and then use the bathroom and touch down there. Don't allow her to eat or drink after others. Don't pick at, pinch or mess with the sores at all. It will only cause more to crop up and may spread it.
For most people a cold sore is not a serious condition. But if they aren't taken care of properly, cold sores can develop into bacterial skin infections. And they can actually be dangerous for people whose immune systems are weakened (such as infants and people who have cancer or HIV/AIDS) as well as those with eczema. For people with any of these conditions, an infection triggered by a cold sore can actually be life threatening. The fact that your daughter has a fever associated with the cold sore is more concerning. If the fever persists or the cold sore remains past the normal 7-10 day period, I would ask the doctor to reevaluate or ask to see someone else for a second opinion.
As far as treatments go, there really aren't any, just relief of the symptoms. She could be given some Tylenol for the fever and discomfort. Also, ice applies to the sore can feel soothing. Abreva is a product that is supposed to shorten the time of a cold sore and soothe the discomfort of the sore. Unfortunately this product is recommended for adults and children over 12. You might check with your doctor to see if under doctor supervision she could still use this.