Google a medical condition called "Quincy." Not to alarm, but mono is often the cause of the lymphatic system going haywire. Often, when very severe, the tonsils become so enlarged they need to be removed to prevent suffocation or choking.
Besides stones as some have mentioned, the thing that is curving into a half circle could possibly be her very infected tonsils. If you notice there is little to no space for the passage of air, get her to urgent care. This is something you should monitor very closely. If it gets worse, or she has difficulty breathing or apnea while sleeping you should bring her to the ER.
In the interim of getting further word from your doctor, do all you can to help boost her immune system. Foods rich in vitamins, lots of rest, and avoiding sick people and crowds are a must to prevent any complications such as another illness on top of this one.
I'm not a doc, but this happend to one of my little ones, and it was very serious. The doctor you saw may be like the first doctor we had, and not recommend laying low and avoiding others. Our child got a second illness on top of mono and his throat nearly swelled shut. He had to have a rush surgery. So be very watchful. Hopefully this will resolve soon. There are cases where surgery isn't needed because the condition resolves itself. But if her system is very taxed or she catches something else, that really does complicate things.
For pictures of severe cases of Quincy and more information see: