Child Unable To Walk, Uses Knee, Foot Indicates Neurological Issues. Suggest?

My 16 month old is not yet walking. She cruises, crawls just fine, can walk holding your hand , and does what we call knee walking (literally on her knees, is able to carry things in her hands and gets around quickly.) Her GP had her start pt and after a couple of weeks noticed her right side is walking perfectly but her left leg has a drag and the physical therapist says there is a weakness in her trunk and hip on the left. She is able to use the left arm equally as well as the right. She can use her pinchers, pick up small objects, color with a pencil. She speaks more than 20 words and a few short sentences (Thank you. More Please. Come here, please. Help, please etc.) Her GP said the drag of the left foot indicates a neurological problem. He referred me to a peds nuero and a developmental pediatrician . However, they won t be able to see us for 2 more months. I did a little research online and found that it sounds like she has monoplesia. She is not cognitively impaired, she does not have behavioral issues. My question is. What are the common causes of monoplesia without cognitive impairment, or reasons a child would not be able to walk and have only impairment of one limb? Are the common causes mild enough that the child can, with the help of physical therapy , completely gain use of that limb?