its completely normal for a child to NOT crawl in the way we 'think' it should be done.
i've known of a few babies who have not crawled but have chosen to use their bums instead.

Im a bit shocked that they want to tie her legs together...it sounds so barbaric and i certainly wouldnt be doing it. Definately get a second opinion before you go ahead with it.

Im just wondering though, whats the problem with the way she's crawling? Is it causing her some physcial pain or are you just concerned that its not normal?