My Daughter Was Running And Felt A Sharp Pain In

My daughter was running and felt a sharp pain in her foot suddenly. When I looked at the bottom of her foot the area from the bottom of her toes to just the end of the arch was a bit red,a bit swollen, and had what looked like sight bruising and encompassed the entire mid section of her foot including the top.she could barely walk from pain. I took her to doc and they gave her prednisone. Took her back three days later for follow up, it looks the same except the"bruising" looks like a big white burn blister. This time the doc gave her benadryl,an antibiotic for bacterial infection and ordered x rays. I do not think they know what it is and are just treating her for different things in hopes something will work. The area does not itch but when pressure is applied she says it's a burning pain that turns into more of a pressure pain.