There is no need to worry. Yet.
Summary of the below quotes:
- Not knowing how to crawl before 11 months old is no reason for concern.
- Place her on her tummy often to build up muscles (but keep in mind SIDS warnings against letting her sleep on her belly before 5 months old).
- Encourage her to move by placing some toys out of reach.
Most babies learn to crawl between the ages of 7 months and 10 months.
Your baby may opt for another method of locomotion around this time,
How to help your baby crawl
Tummy time. From the start, long before your baby's ready to crawl,
give him plenty of tummy time. Placing your baby on his tummy and
playing with him for several minutes a few times a day while he's
awake and alert will help to develop muscles that he needs to crawl. [...]
Incentives to move. The best way to encourage crawling – as
with reaching and grabbing – is to place toys and other desirable
objects (even yourself) just beyond your baby's reach. [...]
Babies typically begin to crawl between 6 and 10 months, although some
may skip the crawling phase altogether and go straight to pulling up,
cruising, and walking. Help your babe get ready for his crawling debut
by giving him lots of supervised tummy time. Tummy time allows him to
lift his head to look around, which helps build strength in the neck,
shoulders, arms, and trunk. When he kicks his feet while on his tummy,
it strengthens his hips and legs. Some babies don't like being on
their tummy, so make it interesting. Place a favorite toy just out his
grasp or lie down in front of him to engage his attention, or lie him
tummy-side down on your chest and talk and play with him. [...]
[...] if your baby hasn't shown any progress in becoming mobile (whether it's bum scooting, rolling to her destination, or crawling) by 12 months [...] it's best to consult the pediatrician.
Most babies master crawling when they are aged between 7 and 10 months old. Some start earlier than that, and others start later. [...]
[...] Spending time on her tummy is important for helping your baby to develop the strength to move her body and hold herself up. If your baby cries when you place her on her tummy on the floor, try lying her on your tummy instead. [...]
[...] Being carried around may not sound like the most effective way of building muscle, but as babies shuffle to reposition themselves in wraps and slings, they are strengthening their muscles. [...]
[...] A couple of toys that move may help to encourage your baby to start crawling. Trains, cars and balls are all great toys that may travel out of baby's reach as she plays with them. [...]
Your baby may start learning to crawl when she's between six months and nine months old. By the time she's a year old, she's likely to be crawling well and exploring her surroundings. [...]
[...] You can help your baby to crawl by encouraging her to spend time on her tummy. There's some evidence that babies who spend plenty of time playing on their tummies are likely to crawl earlier. [...]