Tooth sensitivity

My mom has been saying her teeth are sensitive these days, so we went to the hospital, but they said there is no problem. She can't eat food from the refrigerator and can't eat fresh fruit at all. She also has to brush her teeth with lukewarm water. So she uses Sensodyne toothpaste to brush. The hospital says there is nothing wrong, but she feels so sensitive that it affects her daily life, which makes her very frustrated and worried.