Let me start by saying that my oldest didn't walk until he was 15 1/2 months old. Children walk in different stages, but cannot walk until a certain part of their brain is developed - this much I know.
Have you talked to your pediatrician about it???? I would be shocked if they have not sent you to a neurologist yet just to make sure there were no issues. Personally, I would suggest clearing your mind by taking her to a pediatric neurologist. My son was slow to walk because he had issues in utero that caused him to develop slowly (IUGR).
If that part of her brain is not fully developed, there is nothing you can do to push her to walk. This is why I say you need to check things out with the neurologist. If all is good and it turns out she is just lazy, then I would ask this same question again.
Good luck!