Shanaz, you've got me thinking about this one LOL.
Zara didn't go from tummy to crawling, she went from sitting to crawling. Is there any way you can help her move from sitting to crawling position, and show her you doing it, and coax/encourage her to try it herself? Even after she started crawling, she went from tummy to sitting, then to crawling position, she still rarely does it straight from tummy to crawling.
Also, have you tried from tummy position helping her into a crawling position, bringing her hands under her, and her legs? So although she is in tummy position, you are helping her to get out of it most of the time she is in it, so maybe she won't notice being in that position so much?