She may have what's called a periprosthetic fracture of the femur. The femur is the thighbone. Periprosthetic means the fracture is in the bone next to the implant. The fracture is probably just below the implant and close enough to the hip to be generally referred to as a hip fracture.
Sometimes joint implants crack or fracture but these cases are usually referred to as implant failure rather than hip fracture. Fracture of the femur is not uncommon in patients with either a hip or a knee joint replacement.
Advancing age puts the older adult at risk for bone fracture. Many of the problems that come with aging are also risk factors for fracture. Other age-related risk factors include osteoporosis, diabetes, and arthritis. Anyone who is already experiencing problems with balance and falling is also at risk for bone fracture. Medications such as corticosteroids can weaken the muscles and bones putting patients at increased risk for falls as well.