Left leg moves slower than the right leg

My mother, who is 68 years old, has been complaining for the past few months that her left leg moves more slowly when she walks than her right.Due to this, after walking for a distance, she must stop for a while out of fear that she would fall. After stopping for a while, say for five to ten minutes, she can walk normally for a distance again without any problems. Also, in order to touch down her left leg on the ground while climbing steps, she must exert more force on her left leg. She can't walk quickly like a normal person because her two legs aren't moving at the same speed when she walks; in fact, her left leg is movingmore slowly than her right. As a result, whenever she needs to walk somewhere, she avoids it because of this walking issue. Other than that, none of her legs hurt when she is standing or sitting.Only when walking does one leg move more slowly than the other, which I believe is a result of weakness or some form of numbness in that leg. I need your insightful input