Why Won’t She Walk??

My daughter will be 18 months next week, and she STILL isn’t walking. She has physical therapy monthly, but it’s not much help. She hates putting weight on her feet, and after a few minutes of standing, she seems to be in pain. Just wondering if any one else has experienced something like this? It’s a bit embarrassing having to tell people that she’s a few months shy of 2 years old and still not walking!