What are the chances of a 23yo female to have bone cancer on the side of her foot?

It depends on her Sy: Please tell us about the symptoms and more details of your/her medical history. Bone cancer is uncommon but can occur in your adults. Unless you have a swelling on your foot or progressive pain, it is unlikely to be the case.

Unlikely: Osteosarcomas or Ewing's sarcoma or even synovial sarcomas are rare diseases. There are genetic predispositions to these diseases, but the bone sarcomas commonly occur around the knee or the shoulder, but it doesn't have to be. I'd see a physician if this is giving you pain or other symptoms.