What plaster cast will my daughter need she thinks she broken her femur?

If she really has a broken femur, she may require surgery. She needs to see a doctor ASAP.

Missing data!!!! The femur is the longest bone in the body with potential fractures un upper/mid shaft or lower, just above the joint. It is considered an emergency. Treatments can vary from surgical rod placement to various casts or assistive devices. Without more information nothing more can be said. Hopefully the kid has been taken to the hospital.