First of all, the decision making of knee replacements has some criterias. Age of the patient, severity of symptoms, deformity if any in legs( inability to bend or fully extend the knee or inward or outward bending of knee) and importantly an Xray. Considering your patients age, she is relatively young, then again if the symptoms are severe and if the xrays advocate she may need total knee. Now coming to second question, a properly done total knee with a good quality implant survives for 15 to 20 yrs. Post surgery patient can resume daily activities and will remain pain free. Some of the good companies are Zimmer and Smith and Nephew and Depuy from Johnson and Johnson to name a few. Hope this helps.