Dr O has already given you excellent information and someone has already linked to Hoj's thread about his cham who had the same problem. As has been said, the infection on top of a fracture makes this a very serious issue. It could have been that the infection has been brewing for some time and that's what caused weakening of the bone enough to cause the fracture, like in Momma's case. An x-ray is needed to determine the extent of the bone damage from the infection and how bad the break is. Unfortunately, if the mandible has broken in the middle where it looks like the infection is seated that is more difficult to repair, especially if the bone has been eaten away by bacteria. With the bone broken and exposed in the root of a raging bacterial population it can spread to the rest of the body very easily, which would be life-threatening. Antibiotics are needed asap, and cleaning of the mouth as has been described above. Be very careful opening her jaw for cleaning though - it's already very weak and you could potentially cause additional fractures. But the cleanings are necessary. This is a painful condition that is going to be difficult to heal. Diagnostics are the first step, but be prepared for bad news. Unfortunately you'll need to consider her quality of life here, which is a hard discussion to have. 
