My 3 Year Old Granddaughter Suddenly Developed Painful, Swollen, Tingly,

My 3 year old granddaughter suddenly developed painful, swollen, tingly, feet. They are slightly purple. Tender to touch. Able to walk but it hurts. No reason to suspect injury or allergic reaction. There is nothing restricting circulation. They are warm to touch even though they have been uncovered and it is cool in house. The symptoms are identical on both feet. She has no significant health history and takes no mess. Any thoughts or suggestions?