It looks like Millie may be having an allergic reaction. Allergic reactions can be triggered by things in the environment, vaccines or insect bites and stings but it is often difficult to pinpoint exactly what caused the reaction. The tissue around the eyes and muzzle becomes swollen and hives can develop elsewhere on the body. Emergency treatment with injectable corticosteroids and antihistamines is necessary so I would recommend heading to an emergency veterinarian in your area.