Do some babies bypass crawling altogether? Getting a bit worried about my 7 month old niece who isn't crawling yet.

It is possible for some babies to skip crawling. It is not one of the gross motor skills, such as rolling over and sitting up. It is simply a method for a baby to explore his/her surroundings. The baby could also be sliding on his/her tummy or shifting around on his/her bottoms to achieve the same objective. To try encouraging your niece to crawl, you could place her toy a short distance in her path to motivate her to crawl towards it to reach it. But like what Nooraini mentioned, there is no reason to worry if she is not crawling yet.