Here the symptoms you have mention is lower back pain, lower abdomen pain and thigh pain. All this symptoms are started after hysterectomy along with removal of ovarian cyst. Usually this kind of pain is possible with major ovarian cyst removal for few days but here since its long time over and still she is suffering with pain then I suggest to take secondary opinion. I suggest to do one more ultrasound abdomen and check on abdominal possible issues. If this is normal then you need to take MRI of lumbosacral spine and check report of it. Here if there is major problem with disc or nerve related issue then orthopedic doctor may ask for surgical correction followed by physiotherapy treatment. But if there is no major problem at lower spinal level then you can take her to physiotherapy treatment and along with that take postural suggestion as well spinal exercises. All together this will definitely help her. You can also ask her to use hot and cold pack for her back at painful area for some more pain relief. But if there is problem detected at abdominal level then I suggest as per the issues you need to take specialist suggestion. Remember for conservative management physiotherapy will help but proper diagnosis is also very important for long term relief. Take care.