My Mother, Who Is 75, Was Walking (barely) A Couple

My mother, who is 75, was walking (barely) a couple of days ago and getting around by holding on to walls and door frames. She fell a couple of times Saturday when her knees gave out. We took her to the ER and they examined her and sent her home. They said she needed to eat better and gain some muscle. She is diabetic and concerned about her blood sugar to the point where she checks it 5-10 times a day and doesn't eat enough. Since her visit to the ER she says she cannot stand because her knees want to give out. We think some of it is psychological, she is afraid to fall again. Is there something else we should be concerned about with the drastic change in just a day's time?