Is it unusual for an 8 yr old girl to have calluses & possibly a wart on her feet. What kind of doctor should see her?

Contact Your PCP. Many primary care physicians, fp, ped internal medicine have experience with treating a wide variety of issues including foot warts.Cryosurgery devices (cold application) that use nitrous oxide have been approved for treating warts on the bottom of the foot as well as on other body surfaces. If this is not available at your pcp s/he can send you elsewhere if needed.
Warts aren't unusual. In an 8 year old. Visit a podiatrist.
Podiatrist. See a podiatrist or possibly your pediatrician.