This sounds like a serious situation, and your sister should absolutely be evaluated by an orthopedic surgeon
There are many different ways one can fracture
the pelvis, and the most common cause is trauma, such as a car accident.
In minor cases, the patient may not need surgery
, but may only require a brace and a period of bedrest.
In more severe cases, surgery may be necessary, and the amount of fixation required will depend on the severity of the injury. In these cases, the patient will also likely be immobilized in a brace for an extended period of time (likely weeks).
The particular procedure to fix the fracture will also depend on the fractures seen on the imaging studies performed and the functional status of the patient (healthier patients can tolerate more extensive surgery).
Pelvic fractures can be very serious, and generally have a long recovery period. Patients are often immobile for a period of weeks, and will most likely require some amount of physical therapy to regain full strength and mobility. Some patients will not return to their previous baseline of functional status.
Unfortunately, this is a serious condition, and an orthopedic surgeon should definitely be consulted to evaluate your sister and her imaging studies before any plan for treatment is made.