You can help her along by holding her hands. That will also help stengthen her physically. I don't really see anything wrong with her, however she may just be a slow learner. All babies learn at their own pace. For some reasons, some are just slower at things than others are. There is no explanation for it... just try to guide her along. That is a simple, but very effective way to encourage standing and walking.
She will eventually stand up. Before you know it, she will be walking and you will have difficulty keeping her out of trouble.
