K.C.
Viruses can trigger an immune response that attacks the platelets in the blood. Normal platelet levels vary and can be effected by viruses. When the response is severe it is called ITP (Idiopathic Thrombocytopenia Purpura). The red dots you describe are called petechiae. They are spots of blood. You may notice them on the back side of her knees and around the ankles too. Call your doctor and get her in for a blood test. (I'd do it now). Usually diagnosis will be made based on platelet count.
Typically ITP is a self limiting episode for children resolving within 4-6 months. A wonderful resource is www.PDSA.org. Treatments standards vary from doctor to doctor and country to country. In the US treatment to bring up the platelet level is common, in the UK they take a wait and see approach. My little boy got this at 3 1/2. He is okay now, but it was a scary time for me. Take a deep breath. It will most likely be just fine. If not today, then soon. Best wishes. Please let us know how it goes.