Wearing orthotics help, but I would recommend surgery to prevent damage at the big toe joint. Casting at this point would not help. Since she is young, she would need a procedure that would not interfere with the growth plates, but still allow adequate correction. A closing base wedge osteotomy would work great for her...however, xrays would need to be taken to assess what type of procedure would correct the deformity adequately. Depending on the correction, she may need to be on crutches for 1-6 weeks. Definitely get a second opinion.
Thank you so much for answering my question. I will schedule a second opinion Monday. You gave us some hope.